couldn't Google issue a statement that as of date X any new android licening agreement will stipulate that manufactures release the drivers source code and submit them to the Linux kernel team and threaten to revoke access to the google marketplace and other google services if they don't release the drivers. the manufacturers lost the leverage when they switched to android and the other major non iOS mobile os's died (palm, blackberry, whatever it was call mozilia tried ubuntu mobile etc). now there is only a market for android and ios with sub 1% other.
It's committing the time and resources to get it in a good enough shape to at the very least be submitted upstream.
Embedded device drivers are often developed by cutting a lot of corners, copy-pasting huge amount of code, using magic register addresses that are undocumented and targetting old kernel versions.
Even if they make the code available, there is not much the kernel maintainers can do.
By the time the device hits the market, the driver developers have moved on to the next project in the pipeline. There is never the time to clean up, rebase on top of master, submit upstream properly, and address code review (of you are lucky to get a maintainer to even look at your code).
there already are but unless you have the CPP forcing its use no one will use it as the apps arent there. googles now go the smae vendor lock in that MS does wit windows. no one will wan to pay for all their apps again on another platform.
