That's just a setting choice on most up-to-date cameras. The mainstream film industry likes 24fps because it blurs motion nicely, among other aesthetic reasons. Feature films generally aim for expressionism rather than a simulacrum of reality.

I've never worked in porn but it wouldn't surprise me if 24p is the norm just because it's such a popular workflow choice that it's a highly-optimized default in many video-editing packages, and there probably isn't enough paying demand to support the 2.5x extra storage and bandwidth requirements of 60fps. I'd have thought for Oculus Rift the money would in 3d-modeled games rather than anything recorded with a real camera anyway.