That's because he's part of the agreement.
A reminder to all when the up or down vote comes, the dems on the agreement agreed to vote for cloture, not for the nominee, which is fine (for the bottom line) since we need over 60 to break the filibuster and only a simple majority for the confirmation.
The way they are holding their lockstep party line voting informs me that the time is going to come sooner, rather than later, for Frist to be Nuking these guys. They're going to lose then, for certain.