That's the way the game works, yes. Clearly I understand that. You don't seem to understand my point about the game lacking a reason for the restriction, though. The game doesn't provide any rationale behind restricting unlocked costumes on specific maps. That's specifically what I'm complaining about, and nothing anybody has said has provided an explanation for why the game does that aside from to artificially force you to replay the map.
It's the exact same complaint I have about games with trophies that require you to play through a game or game component multiple time but don't actually add anything to the experience. It's just arbitrarily forcing people to spend more time in the game than they otherwise would.
So yes...character restrictions make sense, it's a story and different people are in different places. Costume restriction...what, Batman just forgot to bring his detective costume? "Shit...I left that in my other belt!"