Often, it's not the simple. Some times it takes months of trust building. Sometimes the person is part of a community, a community they may have been part of for months or years. Yes their life isn't easy, but putting them in housing might remove them from that support network. Often times people are terrified to move away from the only group of people they've known.
Ideally everyone would see the benefits and realize this is better, but these people have a lifetime of other issues and being houseless is only part of it.
this is deeply on display in the "According to Need" podcast series released by 99% invisible recently. https://99percentinvisible.org/need/
Ideally everyone would see the benefits and realize this is better, but these people have a lifetime of other issues and being houseless is only part of it.