It's often not easy or even possible to simply open-source the drivers. What if there are any patents at play? How about third (fourth?) party dependencies? I'm sure the legal would take major offence with slapping GPL on the code and releasing it.

I can also imagine a company like Wacom fighting cheap Chinese copies - I can't imagine persuading the business folks to make the copycat's life way easier by open sourcing the logic.

As long as Linux says it's either mainline or the highway, well, companies will be reluctant to put in the resources I'm afraid.