The core problem is that there are a large contingent of homeless drug users who just want to be left alone so that they can continue to be homeless drug users. Any services given to them will just be redirected by them towards enabling continued drug use. It's like an inbuilt self-sabotage that is totally alien to regular folks, but the choice way of living for those with it.
This isn't talk about much at all, because the story book tale is that homeless people are just regular people who are down on the luck, and if we could just show them some respect, compassion, and spare a few resources, they'd be right back on their feet again. But that story is just a fairy tale used to sell a feel good idea, reality is way more fucked up than that.