It’s because Google are the main contributors to it, and as such have a lot of power over the directions it goes.

Here’s a somewhat decent article I randomly found that explains it a bit better than I can

https://medium.com/@lowharris15/master-of-the-web-how-google-rules-the-internet-with-chromium-65c9e10bd7dd

Chromium is still controlled by Google though, and they way it benefits them is giving them market share and user base. It’s not as direct as using Google, but indirectly still benefits them to have such massive market share with chromium that they can do whatever they want with it. See:manifest v3 and working against adblockers