A lot of them are mentally handicapped or dealing with acquired mental illnesses. Even under good conditions, treating either is hard. Of course EMS/fire fighters/volunteers working in shelters aren't able to do that.
More often than not, we see them a few days later with Steel Reserve cans littered about after someone calls 911 for what appears to them a dead man on the side of the road.
Mental illness is brutal. I feel for these guys, especially as I get older and start seeing my age equivalent homeless folks with PTSD and the like. The Vietnam vets are being replaced with Gulf war and Afghanistan vets. It is heart breaking to be sure... especially because many of us have served. We try, again, to hook these guys up with the VA... but they must want the help. It will not work otherwise.
New treatments such as VR based exposure therapy, or MDMA therapy are promising, but the standard of care is currently CBT and/or drugs, which have generally poor outcomes.
We just don't know how to treat PTSD in general. This has nothing to do with whether people 'want' help or not.
I'm not minimizing their issues, nor am I saying one-size fits all... but I would be remiss to not say: there are a lot of people dealing with mental/medical problems that are resistant to traditional therapies that don't resort to self-destructive behaviour to cope.
To wave off all the choices they make on a day-to-day basis is a disservice them and flies in the face of the people that are dealing with the same issues in non-self-destructive manner.
It's not an easy thing. I have friends who have made it so far, and their struggles were enormous. I have friends and family who didn't make it, and they're now dead. And I know plenty of people who just aren't addictive by nature; they made all the same choices and never had a problem at all.
I get why people don't like this. We all want to believe in the power of will. In particular, we want to believe that the power of our own will is sufficient to the challenges we face. But sometimes it isn't, and if we accepted that, we'd have fewer homeless addicts.
Only if we are the Military-Industrial Complex.
Err... why? Were they on fire? Why is the fire department involved in homeless people?
You've got hospital ambulances, private ambulances, city fire departments, county fire departments, volunteer fire departments and federal fire fighting organizations all potentially in the same place, all summonable by a 911 dispatcher. They all have EMT training and gear. Who shows up and how is it decided? Beats me.
Sometimes human organisation is baffling if you are seeing it from a step further out but makes complete sense when viewed from the inside.