There's far more the kernel devs could do to encourage vendors to free up their devices.
They could refuse to accept drivers that depended on non-Free firmware.
What then? Vendors would then have to decide between:
1. not supporting GNU/Linux at all
2. maintaining Linux drivers themselves, like they do for other relevant OSs
3. freeing up the firmware and getting help and goodwill from the FLOSS communities to maintain them
Yeah, a few might keep on choosing 1.
Some will choose 2, and users will will get Free drivers and non-Free firmware from them just like they would from other OSes, and would be presumably be unhappy about that and prefer...