The killer issue for VR is latency. If you have a lot of latency between the motion and the rendering people will throw up. And it's much easier to control th

The killer issue for VR is latency. If you have a lot of latency between the motion and the rendering people will throw up. And it's much easier to control that latency on a mobile phone platform than on a PC. John Carmack has written extensively on this subject if you are interested. One example he gives is that graphics card drivers will aggressively buffer draw commands to increase performance and image fidelity at the cost of latency. In a normal game that's no problem but that is terrible for VR. Even a little bit of delay between movement and the display reflecting your new position is nauseating. On mobile, the latency can be highly controlled from the driver, OS, and custom hardware even while sacrificing other performance.