1) They could improve those open source drivers.

2) They could improve the other aspects of the experience that is crap on Apple hardware, like display connection/disconnection, sleep/wake, battery life adjustments, keyboard layouts, et c. It takes about a full day to make a mac not suck after installing Ubuntu.

Everything works fine on my MBP except that the desktop is a postage stamp and unusable on the retina display. I tried making things scale but different programs pick up different settings from different places and most look atrocious.

... and sometimes they have even better support than macOS. ;-)

E.g. the 2016 Apple MacBook Pro with TouchBar supports DisplayPort-daisy-chaining, while under macOS you can only daisy-chain monitors if they support Thunderbolt.