Why do schools "admit deny?"

One of the schools my daughter got accepted at CUNY-Baruch wants a housing deposit by May 1st to guarantee housing. However they will not give us financial aid info until mid to late May. Since we are not in a position to pay full price and my daughter loves a different school anyway she accepted elsewhere as much as she would love to be going to school in Manhattan. My daughter applied in October and we did the FAFSA in October and she was accepted late January so I wish we had known earlier about the late financial aid info.