a) Linux doesn't have a stable driver ABI.
b) Manufacturers will not upstream their drivers. It's been years and they simply won't.
Google have been beating against this for years and getting absolutely nowhere. It's the same thing that Linux has ongoing issues with, and have made significant inroads with, for things that aren't tablets or phones. But manufacturers do not want their drivers to be public.
The reasons no longer matter, decades of compromise has resulted in the hardware partners shifting not a single ioata.