You clearly don’t understand software development.

If you’re a programmer, you rarely rewrite a program from scratch if you can avoid it, especially if you’re just making a version update. Do you seriously Epic threw out all their code from UE3 to code UE4 from scratch?

And honestly, Bestesda has done lots of work going through and fixing/updating existing code. Fallout 4 and Skyrim Special Edition are 64-bit programs. Skyrim Legendary Edition and Fallout 3/New Vegas are 32-bit programs.

Updating the Creation Engine to do that requires a ton of changing existing code, but you thankfully don’t need to rewrite everything.

And their work actually makes its way to the players. Skyrim Special Edition is significantly more stable than Legendary Edition, and allows over 10x more plugin files for modders. And Starfield actually held up to the claims that it would be Bethesda’s least buggy release to date