Could you expand on this? I don't follow kernel development closely. Why can't it be upstreamed? Is there something the community can do to modify their code for inclusion?

The DRM subsystem where the graphics drivers live in Linux has a strict open source userland policy - every new kernel interface needs a corresponding real userland implementation that exercises it. So a graphics driver that is only used by a closed source userland blob has no chance of being upstreamed.

And of course just generally vendor kernel code tends to have superfluous middle layers or abuse kernel interfaces in unintended ways.