He said in an interview with THR that it was all Scott Gimple's decision.
So his intention was to go to college and do the show part time? Not sure how that would have worked out, but okay. I think killing Carl was the right move, though. He was basically given
Andrea's
Carl's relationship with Lydia is one of the inciting factors in the Whisperer War. Assuming the writers plan to do that storyline, that is.