You could flip the question around and ask, why do Python and R insist on incorporating emacs functionality in their REPLs instead of keeping things orthogonal. Otherwise, there's a lot of repetition.

As Brandon explained, ghci isn't meant to be the everything-and-the-kitchen-sink development environment.

It used to be that someone starting Haskell would have learned Unix and its ethos beforehand. That's not a ding against you, btw, just an observation that ghci was designed in an earlier era. Patches to ghci are most welcome!