Preference. Some people like their PCs to look like a rainbow alien LED spaceship, others would go for vanta black if they could get it
The beige/brown fans give me a woodgrain vibe more than anything. Straight white would probably be more popular with LED folks imo.
Stuart Semple changed his name to Anish Kapoor, because only Anish Kapoor has the rights to use Vantablack for artistic purposes.
I think there might also be export restrictions, but I'm not sure.