I don't see what any of that has to do with running Android itself. Linux made it big with developers and for servers because it could run on any x86/PC platform. ARM is not a platform. We can't just release a new open source operating system for ARM devices because they're all radically different and non-standard.
There are thousands of models of Android phone, probably over 10k, but to what extent are they all radically different? They all seem to end up using the same chipsets from a few manufacturers, and surely product lines within a single company reuse a lot of code.
I don't think you understood my comment.