It's not as easy as it sounds. Porting things over correctly takes a considerable amount of manpower hours, which is a limited resource for our devs who have such little free time. On top of that, going over to the UE3 engine at this point diminishes the amount of work the W3D Hub team has put into improving the Renegade engine and pushing its boundaries. Looking back at the original Renegade and comparing it to the feats we have achieved throughout our modding history, we have gone so much farther than anyone could have possibly imagined. Looking forward, we do not intend to stop anytime soon!
We can always think to ourselves that it will be easier to go with the UE3 engine or any other, but that defeats the purpose of what our W3D community has been founded on. I hope this answer is sufficient enough.