I literally don't understand.

If Google manufactured all Android phones, and Android were closed source, and Android came pre-installed with the Play Store, Search, and Chrome, I think it wouldn't be a problem, right?

That turns this into an open/closed dichotomy.

Again, they can be ‘open’ (sell/give to other OEMs), they just can’t use contracts to force those OEMs to help them dominate other markets/kill Android competition.

That’s what they’re doing here, just like MS did in the 90s with Windows licenses.

If Android was close there would not be any monopoly, I think this is the idea.

That idea is completely false.

It's plausible that Android would have nearly as many users.

Google, for instance, could have all of the current manufacturers agree to OEM their Android devices. Possibly with co-branding.