I truly don't believe it's the engine holding the Devs back I believe the devs have gotten lazy. Let me think about it how many people bought destiny The original game before it was even out just because it had the name bungie slap on it. how many horrible seasons have we had and yet people keep paying for the next one or for the next DLC. so why put a lot of effort when you can put the least amount of effort and still collect a lot of money.

It would take them 2 years to rebuild in the unreal engine but it would be so worth it... Like going from walking through tar to swimming in water... Weekly sandbox updates. Community support with in game assets and ports from D1 and D2. Stuff like theater and forge.