Unreal Engine 3 and 4 were created around making something that’s great for designers and artists to work in. A lot of older game engines were just designed around having workable level design interface and managing assets/data and that’s pretty much it, everything else was hacked together, stuff hidden in menus, not a lot of options exposed, requiring a bunch of external tools, etc. Lots of older, and even some modern game engines are very archaic, if you do one with wrong in a 5 part import process it breaks, you need tools and scripts to just import a simple asset/texture/model, a lot of basic functionality that should be exposed to artists and designers aren’t, and they have to talk with a programmer to get simple functionality added, which may take 10 minutes if it’s an easy fix, or weeks if they engine wasn’t designed around it.
Unity and Unreal Engine made the whole process much more approachable.