Developers don't blame nvidia b/c they don't want to open source their driver. They blame nvidia for insisting on others shouldering the tech debt of EGLStreams (a closed, proprietary nvidia-only solution with no documentation whose implementation can't easily be tested and verified by compositor authors) instead of enabling the use of GBM with their drivers like every other Linux graphics driver. nvidia doesn't have to open up their drivers for that, AMD's closed source driver (so not the Mesa stack), supports GBM just fine.