He probably realizes that while McCain is actually running for President for most of the year, the Democratic would-be nominees will squander most of that time tearing each other to pieces ... which does not bode well for their party’s chances of winning. One way to resolve it is for the superdelegates to basically just pick the nominee ASAP, tell the other candidate to shut up and go away, and get on with the race for POTUS already.
Dean knows that Hillary will make this a knock-down drag-out win-at-all-costs fight, and that her interests are not necessarily good for the party. He’s saying call the fight and get on to the next one already.
The Dems made a deal with Clintstopheles and now the two-headed beast is looking to cash the check. Good luck with that “closure” Dean.