I’d wager technical debt is the reason. It’s no secret that Bethesda’s engine is bad. Bad code makes it harder to do bug-fixes, because it’s harder to find the root cause of things and the risks of having accidental side-effects is far higher. There’s only so many hacks and emergency fixes you can slap into a codebase before it becomes a house of cards that collapses if you breathe on it the wrong way.