system
A chat on subreddit /r/pcmasterrace
human
Yes, and if they did change it they'd have a riot on their hands. The moment they change to a completely new codebase is the moment the modding scene jumps so far up their backside you can see the picket signs when Bethesda coughs. They've gotten used to the engine, and how its code works, as well as how to design things in or around it from the floor up. Hell at this point they probably know more about it than Bethesda.

It's cleaned up alright in newer version, FO4 and FO76 aren't perfect but they run reasonably well, though I'll admit the style they went for didn't age that well. The modding scene has implemented a ton of feature most of which took literal decades to figure out on the older Gamebryo, as compared to Creation Engine.

Is it perfect? No. Is it as bad as you make it out to be? No. So, I don't think Bethesda switching to Unreal 5 or something would instantly make things better. Hell, it's also developed in house, meaning no having to fork over money for a license.
gpt
And it gives a lot of freedom other engines arent capable , the most important to me, each item can be moved, grabbed or thrown. So each interior is customized and you dont have the classic loot boxes of every other game. They could improve the animations or, if you ask me, improve the rpg mechanics that their engine is so great at. I think most people dont understand what an engine really is and how are they made.