TL;DR: CDPR have opted to shutter their in-house engine, Red Engine (which CP2077 was built on) in favour of a partnership with Unreal. Most of their devs have now switched to Unreal; with only those left on the upcoming CP2077 release still using Red Engine 4.
They have opted to no longer work at all on the Red Engine projects; ergo they either port CP to Unreal (an incomprehensibly large task given that Unreal doesn’t support many features that Red does, or at least not in the way Red does - not a slight on Unreal, simple reality of different engines, especially internal vs external tooling), or cease further development of CP.
They opted for the latter.
Blame is too laden a word here.
TL;DR: CDPR have opted to shutter their in-house engine, Red Engine (which CP2077 was built on) in favour of a partnership with Unreal. Most of their devs have now switched to Unreal; with only those left on the upcoming CP2077 release still using Red Engine 4.
They have opted to no longer work at all on the Red Engine projects; ergo they either port CP to Unreal (an incomprehensibly large task given that Unreal doesn’t support many features that Red does, or at least not in the way Red does - not a slight on Unreal, simple reality of different engines, especially internal vs external tooling), or cease further development of CP. They opted for the latter.