I believe that most carriage agreements have a clause giving the distributor (Directv) the right to renegotiate the terms if the programming changes substantially. If Disney were to simply shut down SoapNet and offer DisneyJr as a replacement, Directv might actually have the right to walk away. So Disney and Directv have to come to agreement on new terms to carry the new channel.
On a side note, I think it's interesting that when Directv moved Baby First to channel 293, that filled up all channel numbers between 290-Disney and 303-TNick with kids/family programming. There's no free channel number in that range to move a new kid's network to.
All they'd have to do is move TV Land to 262, and either put Disney Jr on channel 304 or rework all the children/teen channels within 290 and 304.