I think it's a compounding issue, primarily of Google products just kind of being the "default."

Google pays to be the primary search engine in Firefox, on iOS, and sets themselves as the default on their operating systems. They, wherever possible also set their browser as default. Yes, Chromium is open source, but they have the ultimate final say, and no one seems to have the interest in forking it. This puts Google in a similar position that Microsoft was in in the 90s and early 00s, where they can essentially hijack the web and force their ideas through whether others want to or not.

We saw this with Google forcing Manifest v3, all Chromium-based browsers essentially just had to follow suit. That was just Manifest v3 however, who's to say what else they'll do?

Then there's my tinfoil hat worry that Google essentially being the window to the web for so many people, on an OS, browser, and discoverability level is just overall a cause for worry. That's not even considering their communications and media platforms.