Here’s the thing about a superhero costumes: When you have a solo hero, it makes sense that the filmmakers try to make the costume appear to work in the real world. This is what they tried to do with Spider-Man, the FF and especially with Batman.
But when we’re talking about the world of the Justice League, now we’re entering into a world that is not really like ours anymore, where costumed heroes have become trendy, crazy villains and alien invasions appear every other week, and colorful costumes can be more of an accepted norm.
The X-Men are more of an exception, I think, because they were originally conceived as a team rather than individual heroes like the JLA and the Avengers, and a lot of the problems that the X-Men face are allegorical to real-world issues.