Also, this summer they couldn't do as much cross-fleeting. Next summer, one would think that they'd be able to use the equipment more efficiently, so that would explain why nobody would want to commit to the seasonal flight returning next summer.
I do think that once greater cross-fleeting can occur, it would make sense for them to target a small portion of the fleet to serve increased capacity locations during huge conferences and festivals. Austin during SXSW, etc. Just like they do for the Super Bowl.