The driver ABI is not a part of the compatibility promise, it is an internal API.
However, the folks who break internal APIs also fix the users of these APIs -- if they are available to them. If they are not, tough luck, if you want to keep the driver to yourself, you get to keep all the broken pieces too.
Yeah, I also don't care for that, but I can't argue that that policy hasn't achieved its goals. The Linux kernel has more and better driver support than any other open source OS and also most closed source ones.
However, the folks who break internal APIs also fix the users of these APIs -- if they are available to them. If they are not, tough luck, if you want to keep the driver to yourself, you get to keep all the broken pieces too.