It is perhaps what he chose to do: he sent out Grady and Neald to try find Rand and it's taken much longer than expected. Perhaps he sent one to Caemlyn and one to Cairhien and they both came back empty handed and without a clue where he could be, and he sent them again to track him down, and they haven't yet managed to find Rand, or something has happened to them/ to one of them and they have not returned.

What could delay them very long or prevent their return? Well... Grady and Neald have been out of the loop for quite some time. They don't know about the attack by Asha'man on the Sun Palace, they don't know the last place they should show themselves at or ask about Rand's whereabouts is the Black Tower. It's been a long time since Grady has seen his wife. If he made the mistake of stopping at the BT for a visit to his wife Sara, he may well be dead, or captured by Taim, especially if Grady saw things there Taim doesn't want to get back to Rand.

If they are still with Perrin, what could possibly have convinced him to re-enter Ghealdan and camp near the border instead of Travelling? It could have been an emergency measure at first: he bumped into Galad as he was returning from an attempt to cross the Movlaine and warning Perrin the Seanchan are everywhere there, so they all went west and crossed the border, to hide and decide what to do. Perrin was close to reaching the road in his last scene in TGS, and the Asha'man were still too tired. But why stay in this location for well over a month afterward? Clearly, Perrin doesn't intend to go west either. If he did, Alliandre is Queen and if they reached the cities or the capital she would be able to get help. But Perrin is merely leagues away from the border. Clearly he has stopped and camped "permanently".

Galad's motivations are easier to justify. There is Morgase with Perrin and possibly Morgase refuses to leave Perrin. Galad wouldn't leave either then, especially that Byar and Bornhald think Perrin's as bad as the DO and Galad doesn't have the numbers to take on Perrin's soldiers (nor the will to slaughter refugees or slaugther their protectors and abandon them, no doubt). In this case Galad wants to stay around because of Morgase and Perrin, probably convinced by Lini/Morgase/Gill that Galad always respect his promises, gave one last chance to the WC to do the right thing, despite Bornhald's betrayal in EF in TSR.

Another factor in the calculations could be that Perrin is Galad's best chance to reach the north any time soon and without risking a fight. The way east is blocked to him, the way north is also blocked (he can't go through the Forest of Shadows into the TR and he can't go north some and turn east because of Garen's Wall. The forested area is thick and totally empty of people and there's no way to cross the Manetherendrelle into Andor around there). The way west is difficult at best. There are passes over the mountains of mist in Ghealdan (there is at least one, very close to the border with Amadicia, the one Moiraine and Perrin used in TDR), and from there he could move north of Lake Somal on Almoth and use the passes near Baerlon to enter Andor (or reach the Caralain Grass and TV even, the way Verin has done in TDR), but the Seanchan are on Almoth, Tarabon and Amadicia... Travelling to Andor with Perrin is thus Galad's best chance, especially that he fled without preparations and must be very short on ressources and money to buy any by now (he would have to live on the country and extort what he needs on the way to feed the WC and horses, and that doesn't sound like something Galad would condone... sooner then later Galad needs an alliance to support the WC's needs replace the loss of Amadicia on which the WC organization lived).

Another reason to stay with Perrin is that Galad intends to fight in TG and warned his troops they would have to make alliances they would rather not make, to oppose the Shadow. He had the WT in mind for this, but there's the Dragon too. Perrin would be Galad's best chance to meet Rand to make an alliance, and garantee the resources the WC need.

But none of that explains why Perrin is not moving...

One thing I can think of is that Perrin crossed into Ghealdan because of the Seanchan armies to the east (that part is obvious) and then stopped and has sent the Asha'man to locate Masema. But he didn't seem to care about that one bit in his last scene in TGS (2 weeks or so after Masema's death), and it stretches credibility that in these circumstances Faile, with her sense of responsabiliy as a noble and the welfare of 100,00 people sworn to her and Perrin in the balance, wouldn't admit she's killed Masema, especially that she had reasons to keep it secret on the day of Malden faced with the fact Perrin should have dealt with him long ago and had not, but after spending some time in the camp she would have learned that Perrin didn't care for Masema's survival anymore and even tried to have him and his men killed at Malden (some in Cha Faile, Balwer and co. know this) and indeed got the larger part of them killed, only Masema and his "best men" saw the trap coming and escaped it by moving from the positions Perrin had assigned them for the battle.

It may be there's been contact between Rand and Perrin (through Sulin?) and when Rand learned Masema "has escaped" with his men, he refused to let Perrin's group return and ordered Perrin to hunt him and deal with him, and told him not to send the refugees home, the men at least, but bring them to him once he's found Masema. The "dark" Rand of TGS (we saw Sulin around the time he went after Graendal) might possibly have ordered such a thing (ie: see the male refugees as soldiers, think he's gained another army) but again Faile would not keep the fact she's already killed Masema secret in such a scenario.

Another scenario altogether concerns the Seanchan. Tylee was about to make her full report to her superiors on Perrin and Berelain. A Paendrag heir, a man who command Asha'man and Aes Sedai and is linked to TDR would definitely have gotten the Seanchan's attention - but their big priority at the time was Rand. By the time Perrin may have gotten back his Travelling capability, Seanchan patrols may have found him and an envoy reached him, though. Perrin might be in talks of some kind with the Seanchan leadership. They may have sent him food that let him camp where he is while Berelain has gone to Ebou Dar to meet with Tuon. Tuon might have baited them with allusions she seeks a truce/alliance. Tylee (a likely envoy/negotiator to use) might be fooled, because that's what she would like her superiors to do... Tuon might simply have decided to keep Berelain and Perrin where she can reach them while awaiting the outcome of her meeting with Rand. She would decide what to do with Berelain and Perrin afterward. Perrin may have been using the Asha'man to send the refugees home in the meantime and waiting for the result of Berelain's (or Faile's, or Alliandre's - or the three of them) negotiations. It could mean that after the failure in Falme, Tuon has decided to move against Perrin's army about the same time she's moved against the Tower.

Yet another possibility is that Verin found Perrin before she found Mat and had very convincing arguments to make him promise to stay where he was. We don't know what Verin has puzzled out about the Wolf-King. OTOH, this sounds unlikely. Verin knows the Forsaken are now after the ta'veren and it would be odd for her to advise Perrin to stay in the middle of nowhere when she got Mat to go safely behind the walls of a big city...

The Shadow (Taim or those pursuing Perrin) might have taken the Asha'man out, leaving Perrin stranded. DF/BA with Perrin may have murdered them. They might have been killed in an attack sent by Tuon. But this sounds unlikely. If the Asha'man are dead, then why isn't Perrin moving to a Ghealdanin city where Alliandre could have help. Beside, nothing from Tam al'Thor/Nynaeve suggests Perrin and co. were in a predicament. The big news worth telling for Tam was that Morgase was with Perrin, not "Perrin is stranded and needs help". There seems no urgency at all to convince Rand to send people to get Perrin out of where he is. Not from Tam (who may have been told not to raise this with Rand) but also not from Nynaeve either. It sounds like Perrin is where he is because he has something to do there. Or it could be Perrin was stranded indeed but that Nynaeve/Cadsuane brought Tam back and were organizing things to bring Perrin's full group soon. I guess it would be more realistic for Rand and/or Nynaeve/Cadsuane to have addressed this in this case, but in that scenario Brandon definitely would have cheated not to reveal too much what was going on with Perrin and how his storyline will progress from now on. It would have killed suspense for TOM to tell us why Perrin is still where he is, and if Nynaeve is or isn't about to take care of bringing him to Rand or a city, or whatever Nynaeve/Cadsuane have learned of what Perrin was up to when they fetched Tam. It's a bit mysterious that Perrin has not come with Tam to meet Rand and report to him.


Finally, there's the possibility the wolves are involved in Perrin's decision not to move from where he is. They may be gathering to him by now. If thousands of wolves are coming to Perrin for the Last Hunt, it could be why Perrin has stopped and has no desire to get close to a city at the moment and remains in the Ghealdan forest. He would likely have tried to get his people to go to a city without him, but they might have refused to leave him.

I wouldn't say that Mat's ToM storyline is exactly predictable, but Perrin's is a bigger mystery about which we have far less clues.