Except for Aviendha whose gateway opened in a random place on the other side of the world, channelers got to have a knowledge of geography to use Travelling. The more precise the knowledge, the more accurate the location of the destination. With only basic knowledge of geography, you can't be more precise than opening a gateway in a radius of several miles around the point you had in mind. To be pinpoint accurate (eg: to be able to open a gateway in a "travelling ground" your knowledge of that location must be so great that in fact you need to have opened a gateway there in the past. That's how Rand and the others do it: the first time, they use the "travelling ground" to reach a safe location, then they return using the travelling ground there to their original starting point. Then it's possible to Travel directly from A to B the next times.

During the Breaking, with geography being unstable, it might have been nearly impossible at times to open a gateway accurately for more than a few miles around you. Otherwise you had to take for granted your gateway wouldn't open in a radius of a few miles around the point you wanted to reach (in the AOL, geographical knowledge was likely so precise and well taught to AS they could be a lot more accurate with their destination points), but in a radius far greater than this, from which you would have to make small additional jumps to reach your destination... but that's assuming of course your first gateway didn't get you lost and you had no idea where you ended up, with little choice but to go on blindly from there or give up and travel back to your departure point... if it was still unchanged enough for you to reach it by the time you wanted to return... This would make Travelling far less useful and reliable than it used to be. Those who knew it might still try to use it from time to time, for example to perform an emergency escape or a group decided to move elsewhere and where to go didn't matter so much as no longer staying where they were...but the more the instability of geography and the Pattern went on, the less it would be a priority weave to teach to the rapidly dwindling numbers of new channelers. It's not rocket science: for specialities to disappear, all it needed was for those with the Talent to perform such weaves to die without having taught them; for widely known weaves like Travelling, it's rather obvious that in order for knowledge to disappear requires for the weaves to stopped being used by those who knew it, then to stop being taught. The weave obviously would have been so useful to survive in the Breaking that it follows something made the weave impractical, or dangerous, or even impossible to use anymore, or it would not have disappeared. For the time being it's impossible to figure out exactly what made Travelling no longer useful in the Breaking, but we can narrow it down to two probable causes: either the distorted state of the Pattern made the weave impossible to perform, or the changing geography made it too unreliable or too dangerous to use. The bottomline is that if Travelling was still widely used in the Breaking it would have survived, the same way the crude form of Healing did, therefore for one reason or another it stopped being widely used, and went from there from widely known to rarely known, and eventually no longer known at all.

Don't forget that during the Breaking, the number of female AS went from hundred of thousands if not millions in the beginning to a mere few thousands (the Tower was built to hold a few thousands), and by the end of it no AS who had been trained in the AOL had survived - they were all women who forcibly got rather expeditive training from survivors, and a lot if not all of them not even trained directly by AOLers. Keep in mind that life was very dangerous in the Breaking, and it wasn't just the men, the disasters and all. Shadowspawn were not all gone, neither Forsaken and Friends of the Dark, and there were likely a lot of people who took no chance and tried to kill all channelers they could identify. At the beginning, the world was already in a poor state, with its industrial and technological capacity virtually destroyed by the War of Shadow (at the end, it was already back to using horses for transportation in the center of AS power, the whole "power network" of the Standing Flow was destroyed, making a great deal of ter'angreal useless etc.). Latra Posae seemed to have been able to hold some sort of military/political central power for a while, and to have fought the remaining forces of the Shadow, but even that eventually collapsed, and most of what remains of civilization with it, including the Aes Sedai organization. The next few hundred years were pure chaos.