Hasn't this been discussed like, a billion times? And the answer is always that the amount of work to do it would far outweigh the potential benefits. Besides, these guys KNOW this engine. They know it as intimately as a woman(or man. no judging ). Trying to go from the W3D engine to the Unreal kit is like trying to put a lion in Antarctica. And they actually enjoy using it. It's outdated as hell, sure, but they like it.