That's what I was trying to say, Team-Up films are very different from solo films, and so any in-story explanation of why Hero X's friends aren't showing up is good enough, since the real explanation is that it's just not that type of movie.
Again, I don't disagree, I was just wondering what the excuse was. Even a throwaway line (in either film) about him being busy elsewhere would have been nice, a SHIELD agent telling Nick Fury that War Machine was still 4 hours out, or Rhodey telling Stark he wished he'd been there.
Not that it's a big deal, and I understand that they didn't bother going into it. It could easily become more trouble than it's worth.
The Avengers were assembled by SHIELD. Apparently Rhodes was already working with AIM at that time. But yeah they could have thrown in something like: "No wonder SHIELD didn't call you when NY was on fire, with those new friends of yours!"
You mustn't be afraid to dream a little bigger, darling.