Why are recs absolutely necessary at some schools, while not expected at others?

[HQWest]

My chapter's recruitment already takes 10 days from move in to Bid Day. Rec letters help us to take a chance on an out of state girl or someone that no one knows ahead of time. Otherwise - I think our alternative would be to only take girls that are legacies or those with whom the chapter women have a prior relationship. I cant think of how else to do some prescreening on 1200-1400 women.
The other chapter I was at - recruiment was later, in October, and only 800 women went through, but there was a MUCH higher recruitment drop out rate.