I think people end up homeless due to a confluence of two things:

1. Some kind of addiction (drugs, alcohol, gambling)
-----often (though not necessarily) combined with some kind of mental illness (with the mental illness exacerbated by the addiction)


2. A lack of family or friend support. (Support may also come in the form of money, somehow earned or inherited before (1) started taking its toll.)

For example, take the Dupont Heir - looney as an Arcturian Dog Bird, threatening people with guns and finally killing someone, probably schizophrenic and on drugs, he woulda been on the streets long before he shot his gay lover but for his family money. Or John McAfee out of his gourd on bath salts and committing murder, he woulda been on the streets were it not for his money, which as mentioned another form of support that will keep you off the streets if it doesn't run out faster than your addiction eats it up.

And even people who post online about how they were "couching" at people's homes but broke, would have been entirely homeless but for the largess of friends or family who let them stay in their homes.

So basically, if you have some demon that messes up your ability to function, and nothing or no one to prop you up, you end up homeless.

I don't buy that people end up homeless solely due to bad luck or laziness. There has to be a combo of the above two going on, and that includes some disease of untreated addiction in their brains.