Upstream first policy

Indeed, the user is Google in this case, just like they use Linux in many other places. If Google starts seeing a decline in Linux quality, they will either fork or switch. And to some extend, developing wavelocks behind closed doors could be considered a kind of fork (though on a small scale).

Users actually care a whole lot about maintainability of the code if it affects the quality of the maintenance that gets done. They'll be unhappy if apps they've gotten for their phones start misbehaving when they either upgrade the OS or get a new phone. This comes down to the question of whether the APIs that the apps use can be maintained across changes to the underlying system, and has implications for whether your favorite third-party IM program drains your battery when you're idle online or alternatively stops exchanging audio if you don't touch anything during a voice chat.

If Google's using a design that hasn't passed muster, and they eventually switch to a better design, and the original API bitrots, that ends up impacting users, especially ones who have the idea that they can buy an Android phone with the expectation that any program that they come to like will keep working forever.