I read that the full costume was too large to actually move in, so shots of the full suit in action ended up being CGI. Seems like for the first movie, they built suits that got little to no actual use on an actor.
Certainly for the later movies, they didn’t actually bother building suits, though. In fact, they changed the proportions of the designs to more comic-bookish and thus no longer be feasible as actual armor. (E.g. the legs in the “Avengers” suit were too long, with subsequent movies increasing the size of the shoulders and decreasing the waist.)
