As someone who's been homeless twice, I appreciate that you don't intend to offend, but this is a very loaded and offensive statement. You appear to work with homeless people and have very little sympathy for their situation, which I can understand but it still makes me a little sad.
Becoming homeless is something that can happen to anyone for any number of reasons, and there are different kinds of being homeless. Once you become homeless it becomes harder as time goes on to move back to something permanent. Booze and drugs can sometimes be a simple manner of being able to sleep, or to get away from the situation you're in or how you got there. Choices that seem nonsensical for those who have a warm bed every night make perfect sense when you're worn down by the elements and incredibly poor sleep. After a while the prospect of having to deal with the build up of shit in your life and get shit together becomes a bigger mountain to climb than carrying on when you are, even though your everyday struggle is a mountain of shit in itself.
It's not that people choose a lifestyle as such, it's that sometimes it feels less painful to have a permanent known level of shit in your life than to fight all the way back up to get a permanent place to live and risk being knocked back when you're already pretty fragile. Being homeless is the suckiest thing you can probably reasonably imagine.