Comment by GuB-42

VR is at the intersection of low latency, high throughput, high compute, flexibility and affordable prices.

Embedded systems are often not flexible. They are often designed to do just one thing, like driving an engine, and may run the exact same software for their entire life, which may be decades. They are often limited in term of general computing requirements too.

I don't know HST, but it seems to be similar to embedded: single, highly constrained application, maybe more compute, and I would guess that affordability isn't even on the menu.

Meta VR is consumer software, running on consumer hardware, it runs third party apps, with all the flexibility that is asked of PCs. You can't just put your own realtime OS and claim the entire system for your own specific application.