I think you are misinterpreting this. The problem is that at many schools there just aren’t that many singles. They are in short supply so the school has to somehow allocate these rooms to students who want them. First priority is to those who need singles for medical reasons. Second priority generally goes to upper classmen. Freshman are lowest on the priority list.
If you pick a school that doesn’t have a lot of single rooms, you will need to make a strong case for why you should get one of them. The better thing to do is to choose a school with a lot of newer dorms so that getting a single is not so difficult.