Maybe because many of those who zerg up are required to do so to deal with the rampant cheating and/or immense premade teams? (not specifically talking about DREAM here)
As an example, WL had like 130+ players in their alliance by the end of week 1. We had no choice but to "zerg" in response. This is the last thing we wanted at the start of the server... Your averages in DREAM, whether legit or not, probably forced some teams together that wouldn't have come together otherwise, or maybe just not come together as quickly.
But you know all of this don't you.