That is not why Betamax failed. There was porn on beta. Betamax failed because the cassettes didn’t hold as much tape as VHS and JVC’s licensing model for recorders was cheaper and more straightforward than Sony’s. In the rental market, the format with slightly less friction was a bit more popular each year, which sealed the deal by the mid-80s.

VHS didn't have manufacturer-controlled content purchasing.

The other major VR device manufacturers have a similar approach; you get the apps and content through their stores. Sony, Facebook, Google, etc. are all similarly unlikely to have official porn support; Steam is perhaps the most likely (as they permit at least some adult gaming on their store).

I suspect you'll see plenty of porn apps in jailbreak / sideload world. Quest already has 'em that way.

What's the chances the iPhone will end up like Betamax? It doesn't offer porn apps, after all