They chose to do it this way for a couple of reasons: 1. To help keep the alt-a-holics from having to grind every character thru it in a day & 2. To give the lower level captains a chance to level up enuf to do the episodes and get the first time around special at the end. Yeah, for those with few captains that are already high enuf to do them it kinda sux having to wait, but it' a great thing if your tryin to levle up to do em, or have a buncha characters and limited playtime.
releasing one episode a week, even if the gaps between series is a tall order. they simply dont have the man power to release two or three episodes a week. even if they could crank out episodes that quickly, they still have to internally test them for bugs and make sure there is no problems. an episode every couple of days would just introduce bugs-galore and just be generally of a lower quality.
besides even if they could hypothetically divert all of their resources into making episodes that would mean they dont have time to do anything else, like UGC or episode replay etc etc.
and yes the gap is also there to help people with lots alts.