Lack of competition. Just like Intel and AMD

Intel and AMD compete with each other, shipping raster GPUs.

AMD also ships CDNA, which is a legitimate competitor to Nvidia's hardware (albeit not a CUDA replacement). Breaking up Nvidia into B2C and B2B portions would probably end up killing CUDA in the consumer GPUs (which enthusiasts rely on), and send the value of datacenter GPUs skyrocketing even further. Nvidia's competitors wouldn't benefit from that.