I don't know if you've noticed how high his center of gravity is and how poorly he moves laterally. He might work as a 3 or 4 against strictly bench players, but against a 240-pound chair or a ballhandler on the perimeter with any semblance of ability to break another player down he is a liability. Evans is like a combo forward version of combo guard Price. He's terrific in a pinch and can make an impact on the game with athleticism and effort alone.
That said, Marvin Williams is getting minutes because of his contract and is otherwise one of the most invisible players I have ever... umm... seen.