Performance is probably one reason for the change. UnrealScript was quite slow.
If they added in a standardized scripting language like Python or Lua then they would have to start dealing with porting issues associated with getting those interpreters running on all the hardware systems they are trying to hit. Porting to many different platforms is easier if it’s pure C++. C and C++ are the mostly widely supported languages on all hardware platforms.
Also, removing the scripting language reduces the amount of stuff they have to maintain and unifies the community into using a single language rather than learning multiple (BluePrints are ultimately C++ modules too, so they’re sort of C++ as well in a sense). C++ is the dominant language in the game industry, so overall the decision makes sense.
Admitedly however, visual programming can be klutzy and scripting languages are often more expressive.