It's not about
Don't they know computers work their best using software created by their manufacturers?
It's about maintaining them, nvidia regularly breaks their linux drivers, so does ATI.
And since they are focused on windows or mac, they don't invest much energy on longterm compability with a more complex eccosystem like linux.
about linux and nvidia :)
The idea that drivers automatically are best when produced by the original company is somewhat flawed. It has a higher probability in the beginning but as time passes the company may not think they are valuable anymore and the opensource community often chips in and compensates for this so the open source drivers sometimes will be more stable than the original ones.
But yes :) linux can be a pain