Why Anti-Expansion?

[Firehouse]

Some of the undergraduates at my fraternity chapter mentioned last night that the campus really needs more Panhellenic sororities. There are twenty IFC fraternities of varying size, but only thirteen sororities. All the sororities are large with one exception. We are a large southern campus of 36,000 students, mostly residential. The sororities have big houses and large memberships. There is no shortage of prospects.
Here's where I fail to understand Panhellenic thinking. Since 1960 no new sorority has colonized our campus (one left and came back successfully within a year or so). Almost all are consistently large, strong and successful. No matter how many sororities there are, there is always someone who doesn't recruit well and has trouble.
Since 1960, like clockwork, every five-to-seven years we lose another sorority. Who will be lost each time is very obvious; there is always someone occupying the bottom rung of the system. Low membership is always the culprit.
In forty years we have lost five sororities, at regular intervals, each of whom at one time as large and well-housed. None of those sororities have come back, one assumes because they have not been allowed/asked. No new sororities have been added.
Right now, we have thirteen, and everyone can tell you who is the next in line to go under. There were once large, and they still have a nice big house.
The system is strong, but when pressed for an answer as to why no new sororities, they say 'Well, we can't expand until everyone is at total'. Do they not understand that SOMEONE IS ALWAYS going to be struggling?
It seems obvious, to me anyway, that adding new sororities will bring increased energy and a more competitive dynamic to the system...and might even help the one on the bottom get back up to where they once were.