> Not just locked down
The lockdown is a big part of it, though. The industry has cross-platform VR/AR SDKs like OpenXR that Apple refuses to implement. A big reason their platform isn't supported day-and-date with multiplat VR releases is Apple's insistence on reinventing the wheel with every platform they make.
If the rumors of Valve's VR headset being able to run flatscreen games are true, it's more-or-less Game Over for the Vision Pro. The appetite for an iPad-like experience with six DOF is already handled by much cheaper machines.
Many creative people don’t care about being “locked in”, since they already make mods that can be broken by updates (and often are, unintentionally) and threatened legally (for violating IP and DRM). I think the much bigger problem with locked-down engines is simply that the lockdown methods used make it harder to develop on them.