So I've been playing Tropico 4 for a bit, and it looks pretty good. You're always zoomed out, so you don't need to have more than like 8 polygons for a limb.
I literally could not run cities Skylines 2 or KSP 2 at a good frame rate. Everything was modelled incredibly well and looks great, but that doesn't mean shit if I can't run the game. I strongly suspect that's a big contributing factor.
In addition to this, they're going to against their biggest competitors: the previous game. It's literally the same game with more content, runs incredibly well by comparison, has a huge mod library, and is much cheaper to boot. Might not be as pretty, but it actually might not matter given what you're playing.
I think there's probably a lot of issues that contribute to this to be honest, but it feels like at it's core it's a fools errand to begin with.