What if we pressure Qualcomm and ARM for 20 years but they still don't upstream anything? What about 50 years? Would you change your position?
Eventually the community will write their own drivers (as has happened with Mali) and the respective vendor will have a reckoning internally (like what happened with AMD's GPU driver) whereby those advocating for wasting money on out of tree code leave the organization with egg on their face for bilking the company out of significant R&D cash.
It is very hard to claim that its worth it to develop a proprietary driver when a comparable performance driver already exists for your hardware in-tree. The in-tree driver will almost certainly be easier to use & break less often than out of tree code that the kernel devs don't think or care about breaking.