It's keeps them from organizing. If you let a camp sit long enough, it may become somewhat stable. The people living in it might get resources that they would otherwise have access to. It might even been seen as a partially good thing by some of the locals with housing. This is potentially beneficial for everyone except the cops, who will have a harder time moving them when someone influential enough wants them moved. So you have the massively wasteful, dehumanizing, and likely unconstitutional system that exists now, because it makes cops' jobs easier in theory.