This isn't just a team-up; it serves to move everyone forward to a new dramatic place from which to launch the next round of Marvel Studios films, as well as providing a launching point for the starts of new franchises.
Jon Favreau approached Avi Arad with the intention of making it a comedy, but luckily opted to make Iron Man instead. Then, Incredible Hulk director, Louis Leterrier, was shown concept art and offered his services, but Marvel turned him down.
Captain America was the first of Marvel's characters to get a second chance with what is, essentially, a hard reboot that completely ignores both of the television movies that came before.