>>281356219
This. Cosplayers don't get changed together in a room like that, they come to the convention already wearing as much of their costume as they can be, and then do final assembly on site as needed. Getting into or out of a costume fully can take up to an hour, depending on makeup and how many little fiddly bits you have to get perfect you have. You don't wait to do all of that at the last second on-site.
Think of it this way: if you came to the convention in normal clothes, and you change into something else entirely... where do you keep your normal clothes? Are you just going to carry them around with you, everywhere you go all day, for the whole convention? If you had a hotel room to drop them off in, you'd just get changed *in there* before you can down.
