The double year teams are just bigger. You have all of the 05s and half of the 04s. Even if you did nothing more than keep everyone who played last year, you would end up rostering at least 25.Considering 05/04 they're probably trying to get as many players on the ECNL team (not ECRL) as possible so they're more marketable to college recruiters.
Or maybe players arent very committed so they're just making sure they have enough to field a team week after week.
It may not matter by then. Playing your last season on one big team is probably more fun than watching five of your friends get cut.