Honestly, even costumes people think of as "form-fitting" usually aren't actually. They're often not really skintight, but padded to give the illusion of someone muscular wearing a form-fitting costume.
Even Quicksilver's AVENGERS costume has wrinkles and creases in it, too, despite being the kind of thing people seem to want.
And I would argue that this Flash costume IS pretty form-fitting. Just because it has some wrinkles or creases doesn't make it not a form-fitting outfit. It's clearly tailored to his body, his musculature, frame, and quite tight to it in most respects, other than where he needs to be able to move explosively.