Hard to debate when you have already selected your nominee.
It’s to figure where enthusiasm will come from...not just for Presidential candidates, but all the secondary candidates (senator, house of representatives, governor, sheriff, etc). If they decide to skip debates prior to Iowa and hope to skip them entirely...fine, but it’ll be low turn-outs for the whole primary period across the board.
I do agree...with one single debate...Bernie might wipe out Hillary’s marginal support.