The point is that distro patches are trivial compared to Android patches. Your distro will continue to work fine with a vanilla kernel unless it's using an esoteric configuration, and even with esoteric configurations it's relatively easy to include necessary patches to vanilla kernel.

Compiling and using a vanilla kernel instead of the distro one is straightforward and easy job for people with basic knowledge of source building. It's not a job for "very few brave souls". The reason many people use distro kernels is because they're good enough.

OTOH any consumer Android device requires millions of loc patching to a several years old version of Linux kernel just to boot.