Why doesn't anyone else use PowerVR?

This is one thing I've always been jealous of. The one thing where Apple always annihilates the competition. A Power VR 6 series in the 5S is going to be king for a very long time, nothing else will come close for some time. Why do Android phones almost always have inferior GPUs? And it's not like Apple owns Imagination Technologies! Why don't more vendors choose PowerVR, if they're so far ahead of everything else?!