AAA studios were used to having local build farms, in-person build-review sessions, and testers being in the same physical space so engineers could see what's going on. They have collections of unreleased hardware that need to be distributed and secured.
It's not simple to completely overhaul a setup like that and go full remote. You're moving 100s of GB a day to each dev and trying to change every one of your processes.
Every AAA engineer I know complained about how how slow everything was remote. Studios are figuring that shit out now, but I don't think "hurr durr Todd Howard old" is really accurate or adding anything to the conversation here
This is nowhere near reality.
Even if you could just "translate" code from one language to another, that ignores asset pipelines, asset store libraries, and all the build pipelines that allow you to ship cross-platform.
You also need to now train your entire dev team on a new tech stack.
Switching engines is an enormous effort