Well a big part of homelessness is substance abuse and mental issues.
I know a whole bunch of people who've been homeless, sometimes for up to a year sleeping on the streets. But they'd eventually find their way and move on. In the developed world, there's so many programmes. They're not fun, don't get me wrong. For example you can get a bed, a meal and a shower, but you have curfew at 8pm to reserve a spot and you have to spend the night with a bunch of strangers, not all of whom you'd want to hang out with, and then you get thrown out at 8 in the morning. None of that is enjoyable, but you can do it. Then you can apply for a home, you can apply for a free public transport pass, and you can pretty easily get minimum wage jobs. None of those are great, but e.g. in the Netherlands minimum wage is about $1700, and you get 1 month of mandatory, by law, of holidays per year working full-time, in which you get your salary. This is liveable for a person without children, and combined with all the different programs it's impossible to not live a decent life.
But that's for an ordinary person. If you have a gambling addiction, a substance addiction or a mental issue, none of that matters. You could squander a $10k salary, or have days when you're too scared to go shopping for groceries.
Short-term homelessness is very solvable, I've got friends who've gone through it. Long-term usually is much tricker because you're not dealing with a 'normal' rational human being. These people simply need help, lots of it. It's not a matter of giving a person a job, clothing, a home, because they can't function, none of that helps. They need professional help, and the resources for that aren't being spent. Instead resources are largely spent on keeping people alive.
Of course there are tons of exceptions. I've got a family member for example who was homeless and was really stuck due to a lack of programs available to get him back on his feet. In the end he was 'saved' by the grace of a total stranger, given a place to sleep, food, shower etc and support in becoming self-sufficient. He was mentally fine, educated etc, but ran into one of those 1 in a million odds that destroy your life. And the stranger helped him out. But he's very much the exception. Most are like another family member I had who simply had substance abuse issues. We took him in over and over, got him totally setup after 1-2 years of homelessness. And he'd be right there with us looking handsome and sharp and jolly, nicely clothed and cleaned up, and he'd be sharp as a knife talking about politics. Everyday we'd give him a few bucks for some cigs and a newspaper and stuff, and have him eat all his meals with us and sleep with us. And then 3 weeks later he'd be gone, and we'd spent months on the streets just walking around asking people if they'd seen him. Finally 1-2 years later we'd find him and take him in again and it was the same story, every 1-2 years it'd repeat. But he just couldn't live that life and always fled. In the end he'd be gone again and we went looking once more, but this time he died on the streets, we don't know how. There's nothing you can do for him but get him professional help to deal with substance/mental health issues. I suspect most long-term homelessness is like that.
It's always so hard for me to decide which it is... I've experienced both, people who you simply can't help, but only professionals can, and people who you can totally lift up and get back on their feet with a little bit of trust and resources.