That’s because you think his staying in helps Trump. If you were confident about Trump winning no matter who was in or out you wouldn’t care if Carson left.
Why give the GOPe the opportunity to gain momentum?
But to the extent that Carson can pull votes from any of the other candidates and keep them below the "Threshold" for getting any delegates, it increases the liklihood that Trump will win the majority of delegates and be able to claim a state as one of the 8 necessary to get nominated.
So I'm not sure, but yes I think it helps Trump but not in the way you were thinking.
Although Dr. Carson is not my first choice, he has made a number of comments that needed to be said. I also wish Fiorina and Christie had stayed in. I liked the former taking on Hillary and the latter added spunk and humor. The take-down of Robot Rubio will become a classic.