It's just risk aversion. Companies want to turn video games into a factory line golden goose, but struggle to reconcile that each iteration through that factory line makes the final product relatively worse and worse, even if it continues to look better and better. Now even Call of Duty can't find a Call of Duty killer. But these same companies are terrified of trying anything new because new things do, on occasion flop. It would also entail scrapping the factory line, because creating a new game, instead of reskinning and old with a few new tweaks, is a way different beast.

That said, I don't really think the stereotypes of indie games are very valid anymore. Valheim looks great, has a massive open world, and is multiplayer. [1] It also started entirely as a result of one guy's pet project, until he grabbed a coworker and then set off to make it what it became. The graphics are stylized, but I think in a broadly aesthetically appealing way, as opposed to e.g. pixel graphics which are very off-putting to many people, myself among them. Pixel graphics came from an era of CRTs with interlaced scanning, and various other visual artifacts, that naturally blurred, antialiased, and blended them. Sharp jaggy edges never really existed, and I fail to understand why that's a popular style now.

[1] - https://www.youtube.com/watch?v=XSVbXgBJIuI