I have a few family members that are homeless and with good reason.
They basicaly would not listen to reason, and drugs was the main motivator in their decision making process.
You can only lie, cheat , steal and hurt everyone you know for so long until nobody wants you around unless you want buckshot in your behind.
Not alot of people choose to become homeless but their actions lead them there once they have exhausted all recources and fried their brains in the process while making enemies with everyone they know.