I would bet this CPT DLC and the costume stuff has been in the pipeline, and they could have been sitting on it for a while. They could still have a backlog of originally planned stuff and not far enough along in progress on the new fixes and modes that are needed.
This is correct. The torrent of DLC we're getting only seems like this because the Zenny system's failure delayed the premium costumes. If the store worked Day 1 we would have had premium costumes Day 1 and the release schedule of DLC would have been much more spread out.