They already have once though. Many of Morrowind’s dungeons were procedurally generated in development then edited a bit after, that was the same engine. Same with Daggerfall altho that was a diff engine.
Very different game but Amnesia: the Bunker has plenty of procedural generation as well.
It’s not at all impossible for one of the largest game development studios to have some procedurally generated, essentially dungeon content. Doing a bit more than the exact same place copied and pasted would be a huge undertaking yes, but if they wanted to they could have. There are plenty of 3D rogue-likes out now as well. Returnal is AAA and haa procedurally generated levels, far more complicated than neccesary for Bethesda to do in order to populate planets in their game about planet exploration.