Possibly it is hard, tedious, or the people able to fix it don’t think it is worth the effort.
Open source projects rely on volunteers mostly so it isn’t like there’s some outside force to appeal to. If nobody volunteers a solution, then it isn’t important enough to solve. The point is that, if it were important enough to fix, anybody with the requisite skills could do so.
With open source and mainlined drivers, it's very difficult to change all the drivers and ensure they work.
Without open source and mainlined drivers, it becomes impossible.