Because they want to do something more visually unique and interesting than just an old fashion cotton or spandex suit.
But that's just it -- when practically
every superhero movie and TV show for the past couple of decades has insisted on making superhero costumes out of that weird rubbery material with basketball texture and gratuitous ribbing, it's not even remotely unique, just tired and predictable. At this point, going back to simplicity and practicality would be far more distinctive.
Detailed costumes are fine if there's a sensible, functional reason for the details, if it makes the costumes look more like practical action gear serving the heroes' needs. What Superman needs is something he can hide under his street clothes, and that's about it.
I like it, it's a lot more visually interesting than just a big plain S on his chest, which honestly would look kind of cheesy these days. It might have worked back in the '50s or '70s, but not in a modern big budget serious, or at least seriousish, movie.
I don't see why Superman's logo looks cheesy, any more than the
Enterprise arrowhead insignia or a sports team's logo or the American flag. It looks the way it looks because it's his established symbol. The fact that it was designed a long time ago is exactly what makes it iconic. To me, it's a meaningful symbol standing for a character that inspires me, in the same way the
Enterprise insignia is. In-universe, it's generally defined as a Kryptonian symbol meaning "hope," and that's basically how I see it (although in the Arrowverse it's called the
El Mayarah and means "Stronger together").
Also, the "it looks cheesy" argument is the same reason people wanted to get rid of the trunks, even though they kept the equally "cheesy" cape, logo, and boots. Now the traditional trunks and belt are back, yet it's the logo that's too "cheesy"? I don't understand the cherrypicking.
Besides, this version of the logo is far too oversimplified to be visually interesting. It's like how Google and other companies keep streamlining their logos to the point that they're virtually abstract and don't look like anything anymore. This is little more than a pentagon with a diagonal line. It's almost generic.
But for me (and probably the JLA/Avengers folks), that's part of the operating premise of these superhero worlds: that the fake stuff exists alongside all the real stuff, not in place of any of it.
Except that was obviously not the case where
The Atlas of the DC Universe was concerned, or that earlier comics panel that initially established the locations of Metropolis and Gotham. That map established that cities like Philadelphia and Baltimore existed, but that Dover did not because Metropolis was in its place.
And it's not the case when comics or other works of fiction establish imaginary foreign countries like Kahndaq or Latveria. The maps always show them as occupying territory that belongs to different countries in the real world, so that the real countries have to be smaller to make room for the fictitious ones. The usual premise is that the real-world places exist
except where they don't, because they have to make room for the fictional places that are relevant to the story.
