@tomie new engine, inexperienced devs, incompetent shareholders/publishers. Even with ue4 there are STILL games that stutter all over the place and that can be mitigated but just isn't. If you look at fortnite, it doesn't really have these issues and that's because it is developed by the people who made the engine.

I am also of the opinion that just in general, not just in unreal, devs are pushing systems way too hard and not optimizing things very often. That can come as a result of publisher intensity, but there's also a certain point where it's obvious that the devs are relying too heavily on hardware that doesn't exist yet, or features like upscaling (the finals doesn't let you play without some kind of upscaling tech as far as I can tell, which is crazy).