It would be interesting to see how many people they have to turn down for looking too good.
It seems to me that, "ordinary," women, even the attractive ones, have relatively low self-esteem (given the current media culture of, "beautiful people," who can blame them?). It would not surprise me one bit if the agency got plenty of beautiful women who thought they were ugly, that would have to be turned down, or given another job (on the plus-side).
...maybe it's the most effective strategy from both sides.