> Other than inertia, and an overrated idea that proprietary drivers give you a "competitive advantage" over your competitors' very different hardware, why aren't more manufacturers making open source firmware for their hardware?

While this is arguably true for most hardware, GPUs are different from mundane hardware like ethernet adapters. The driver source code will reveal secrets about the hardware architecture, and the architecture changes in every generation. The advantage is not in the software itself, it is not showing the cards you are playing with.

In theory, it would be possible to give out the source code to the video drivers but it would not make sense to give out the source for chips in development. At best, you could get source code dumps after a new chip has rolled out. This is not really open source.

Yes, I want quality open source video drivers but on the other hand I want bleeding edge hardware and competition that drives hardware development.

Disclaimer: I write GPU drivers for living and I'm an open source enthusiast.