Originally Posted by herolee10
Well someone pointed out that if Stark is really going under the radar in order to go up against Mandarin, then it'd be difficult for the likes of Banner and SHIELD to track him down and help him; and it's more likely possible that Captain America and co. will be busy with their own missions around the same time and Thor is more likely occupied with the Asgardian war taking place in the other realms as well.
Best explanation is that they're all busy. Their respective solo movies will be the proof. lol