Probably due to Namco wanting to artificially extend the game's lifespan by now releasing the catalogs on a bi-monthly basis so that there's not much of a gap between im@s 2 and whatever they're cooking for the PS4, Vita, or whatever. Just speculating, though.
I wouldn't see why, though. They have enough old songs to keep going until well into next year. And it seems like a lost opportunity to have skipped this month. They could've easily done a LaLaLa Wonderland catalog with the Puchidolls as accessories (like in SP) now that the season (series? ;A;) is done.
