At the risk of inciting a flame war, I'll politely suggest that, while they're usually good enough, I'm not sure I'd say that AMD's drivers are quality. Not to belittle their engineers, only that I've seen enough issues to not prefer AMD for the quality of their drivers. The fact they're mainlined and FOSS is a big bonus, but that's regardless of their quality.

Beyond that, some of us need/want CUDA or other GPGPU support, which is a total nightmare with AMD GPUs, and other times the price/performance ratio leans in favor of nvidia, or some people just have nvidia cards and can't/don't want to buy new ones.