From the few directors I've spoken to, it's a typically a lack of time, budget, and effort. VR also complicates lots of things that are taken for granted in flat porn.
It's far easier to pump out scenes on a conveyor belt and for the general public, that's good enough. You can spend the time to craft a 3 hour epic or you can knock out 3-4 smaller scenes that are safer and more reliable.
I think at this point, our best hope is to wait for the barriers to entry to get lower so the people with the desire to make certain kinds of scenes have the resources available to do it, because waiting for any of the current studios to make something outside of their formula is just an exercise in frustration.
Everyone wants to be an innovator in VR tech. No one wants to be an innovator in VR content.
