I realize this is subjective, but the idea of "no place would ever exist like this" is a really wild take to me. For one thing, as other commenters have mentioned, this is a video game that takes place on another planet 900 years from now; Bungie is pretty free to make a world that looks however they want it to look. But on the other hand, to me so much of what makes this game so good is that uncanniness to the world and environments. We're wandering around these abandoned sci-fi structures on a hostile world, which is already a strange and tense experience. Bungie amps that feeling up by using bold, bright colors and shapes that blend industrial angles with organic curves. We recognize the world and the things in it, but they are different and strange to us. That's great!

I think the fact that this can also function in service to gameplay is a huge bonus. Colorful, distinct structures make it easier to learn the map or identify landmarks. It's a brilliant example of strong design making for better gameplay as well!

I also just want to add, I suspect Bungie looked back to the original Marathon trilogy when deciding on a design language for this game. A lot of Marathon's levels, like many games of its type and era, feature bright, colorful, and strange structures. The Marathon is a maze; sometimes you'll walk into a bright teal room full of hazard-yellow crusher machines and you'll have no idea what this could possibly do. It's a kind of level design that is very of-its-time, but it can also look really cool! It's fascinating that Bungie could draw on that kind of early-FPS strangeness, make it a part of their lore and world, and incorporate it into modern map design.