Google offer the Google Platform to people who agree to certain things. But anyone is free to fork Android at any point, if they choose - Amazon have done so, for instance, as well as many Chinese manufacturers.
Many AOSP applications have been abandoned by google in favor of their proprietary applications.
There remains nothing stopping you replacing all the Google stuff on Android, including the very parts that make them money.
One of the sadder, non obvious, parts of the way mobile has developed is it is becoming synonymous with trivial front ends to cloud services, and not really smart client apps at all.