Vendors still make generally minor changes to the kernel, but these are not unique or special or some competitive edge. They've just nuisance necessities.
That reasoning doesn't apply to most kernel drivers, and those vendors are just openly in conflict with the GPL.
On top of that, GPUs generally have to have a kernel component, even under systems that put as much as possible under user mode like sel4, because they have their own MMUs that can subvert kernel integrity.
Nothing of that prevents that all new drivers, except for the ones marked as legacy, are required to be Binderized.
The kernel code of a driver from OEMs allergic to GPL, is hardly different from a signal handler, implementing the minimal set of kernel code and deferring everything else to userspace.
You hinted that this transgresses the GPL, and there are those that argue that virtually anything transgresses the GPL. But a lot of very large corporations say otherwise, and there have been zero successful challenges against it.
