Your answer is in your question, CVG. Delta's unwillingness to offer reasonable fares have forced the business traveler to other airports and airlines. Why pay Delta's price for CVG flights when you can use Airtran or even Delta out of Dayton for MUCH less?

Case in point:
CVG-MSP midweek RT: ~$665 (DL, NW)
DAY-MSP midweek RT: ~$275 (DL, NW, Midway)