The OS itself doesn’t serve ads, but rather the apps you install and the web pages you visit.
I don’t know what phone you use, but a stock Samsung phone absolutely serves ads and tracks like crazy. You can monitor the activity with something like Adguard. Not to mention the bloat like Facebook will call home even when you aren’t using it.
So yeah, it would be nice if the OS itself wasn’t an open door for this type of crap.
Aaaaaand, you lost me.
I’ve got so many spare phones that I’d love to install this on. Not a single one is from Google. They screwed me once with their hardware (Pixelbook), and I don’t feel like giving them any more money.