ID tech is nowhere near flexible enough for something like Starfield or even Skyrim. It’s partially the reason why it’s so efficient. It simply isn’t fit for the task.
And the Bethesda developers are intimately familiar with Creation Engine, achieving the same level of productivity with something new will take a long time. Switching the engine is not an easy thing.
Not to say that Creation Engine isn’t a cumbersome mess. It has pretty awful performance, stability and is full of bugs, but on the other hand it’s extremely flexible which has allowed its games to have massive mod communities.
Beehaw’s reasons for defederation were completely unrelated to what’s happening now. They didn’t want the general public to have access to their “safe” community.