I think it has something to do with preventing people from running the higher-stability drivers that come with buying a Quadro (or hypothetical super stable FOS

I think it has something to do with preventing people from running the higher-stability drivers that come with buying a Quadro (or hypothetical super stable FOSS drivers) on significantly cheaper consumer hardware, because that makes it much more difficult to justify buying a Quadro in many circumstances. The added stability is part of the upsell and is more software than hardware.