Base Android (AOSP) is not, what you probably mean is Google Android.
Look at GrapheneOS, that is a usable, privacy-focused Android without bloat.
Almost none of the devices are shipped with anything but Google’s Android, and manufacturers don’t provide you alternative versions of Android
Yes, Google owns Android as a whole, but (almost?) every single OEM customizes Android for their purposes. That is not the same thing.
I’ve used it for many years. Lineageos is a largest rom sure .
The issue is that google fucks with base android more and more. Now they made it that there is that yellow logo on boot - your android is insecure. Then banking apps are not working.
Updating from android to android on lineage was a chore on oneplus 8t.
And I ended up not being able to rollback to stock because I wanted to trade in for A new model.
It just makes it harder to use roms.