People who are addicted or who have given up to that degree are less likely to want help if they think real life can only be totally miserable for them (like, “the world is unbearable, there’s nothing good left for me except [drug name here]”). Same reason people who are depressed turn to drinking. Making the lives of unsheltered people even worse, thus making drugs more appealing in comparison, is counterproductive. And the longer they’re stuck in that, the more that’ll just feel like what life is to them.
Maybe people who don’t want to, or don’t act like they want to, better their situation actually would if they could see any hope for it, and if the path looked more doable and less like scaling mount everest with a broken leg.
I think anybody can think of times they didn’t want to do something that would benefit them - clean a house, do their homework, go to work in the morning - and other times that the situation was different and so it was much easier to do.