I'm pretty sure the reason is that VR is not just regular games but in 3D. Instead the games have to be different in many aspects. Most people cannot play with those goggles for longer than half an hour. You have to address that. Also rendering 3D with comutation constrained to what's in the goggles is placing serious limits compared to rendering (3D projected onto) 2D using a much heavier hardware requires game development to rethink the entire design of a game.