We do manage to spend a quarter billion dollars a year on homelessness in San Francisco, amounting to tens of thousands per homeless person. And that doesn't even count costs that hospitals and medical centers have to spend on ODs, various stabbings, etc. So finances aren't the issue.
If I had to identify the issue, it's that there's a lot of status quo players who comfortably exist in the current state of things (after all, that's a lot of money floating around). The people who suffer worst from the state of affairs (the homeless themselves) pretty much have no political pull or people looking out for their well-being, and the rest of us get shouted down if we complain about having to step over used syringes and human shit as we open the door to our apartments every day ("you think you have it bad? Think how bad they have it!")
Last month, I was walking through SoMa with my boyfriend, and a homeless guy literally came up and punched him in the back of the head for absolutely no reason at all. He walked off, we called the police, an officer came, and his response was basically.. "well, what do you want me to do about it? There's no point in arresting him." Even though the perp was standing on the corner like half a block away.
As a city, we need to decide whether the homeless are autonomous people who can be held responsible for their actions, or whether they are desperate souls who really can't be expected to care or look out for themselves and really don't have any "rights" beyond being treated humanely and compassionately. Only the latter really makes sense in my view, but this in between place of "they can do whatever they want no matter the ill effects on the community, but we're morally required to continue to throw hundreds of millions of dollars at their self-described champions every year with no improvement in the situation" is ridiculous.