The last thing spiderman needs is to join a team with a rich pretty boy running it. He hasn't exactly been treated well by them in the past...
He was turned down by Batman to join the justice league why would spiderman join the Marvel equivalent of him??
Also, while Ironman did give him an Ironspider suit, it only had 3 arms! What's up with that!?!? It should have four arms, Spider-mans own villain Doc Oc knows that why doesn't Stark??
TeamCap will treat him right and make sure his upgrades are up to standard. Also, Captain America is much more handsome than Stark and I think @shannonl5 would agree. Lol Plus, we got cookies ;)