The roof also comes with a loss of any sense of personal autonomy and the threat of violence from other people in the shelter.

There's a reason people treat them as a last resort, and it's not drugs. It's that being in a shelter opens you up to abuse.

Those conditions make the offering quite different from being able to rent your own room inexpensively. One of the facets of having your own place is that you can do whatever you want there, whether it be drugs or whatever. That might not be healthy, and it's quite understandable why family would put conditions on offering a free room, but people do value their autonomy.