Unreal Engine is like the McDonald's of game engines and also has its own issues (Batman: Arkham Knight, anyone?). You won't see Larian Studios abandon their own engine used for Baldur's Gate 3 any time soon, nor will EA abandon FrostBite or Ubisoft do the same with AnvilNext or Snowdrop, or even Bethesda themselves with idTech for Doom: Dark Ages. Beyond the visuals and maybe the blueprinting style of connecting programming modules and scripting together, what does Unreal Engine really have to offer that others can't?
One potential advantage of being in-house in Microsoft now is having more dedicated resources to constantly improving the Creation Engine 2, if they are wise enough to use them. Even (shock, horror) licensing the engine out for third parties looking to create their own Skyrim-like games would help drive this.
