> An ABI for the people who cared about that random driver might localise the maintenance burden.

Yes, but one key reason that a stable ABI isn't provided for drivers is to help encourage companies that ship drivers to make their drivers open source. The idea being, if a driver is mainlined into the Linux kernel, the Linux developers will help maintain support for that driver, in exchange for it being released with an open source licence. There are companies (like NVIDIA) that ship closed source drivers for their devices, but they rely on a kernel-side shim that interacts with the userspace driver, and this is seen as second best compared to mainlining the driver in the kernel.