The reason they're hellbent on improving their existing engine is they have the biggest modder community out there. Their day 1 releases are always buggy as hell and crash to desktop bugs a year or three after release are still plenty, but I actually love their overall technology.

They do need to fix their physics and modernize frame rates and aspect ratios but other then that I hope they never change to some completely different engine. Loading in Bethesda games is always much faster than most other games too.

But FO76? I'm going to pretend it doesn't exist, they might as well have just released it as a DLC for FO4 because it seems completely pointless as is.