There's a witch's brew of reasons for this. A lot of those who persist in living on the street are hardest to help, for reasons that often involve medical issue

There's a witch's brew of reasons for this. A lot of those who persist in living on the street are hardest to help, for reasons that often involve medical issues, psychological issues, addiction issues, or a general aversion to getting off the street. California makes involuntary commitment extremely difficult (for good historical reason), so people who refuse help or treatment don't get any. SF is also incredibly bad at making use of a vast pool of resources. The amount of money spent to help the indigent is substantial, but no amount of ineffective spending can address real problems. Other changes that might help, such as constructing homes for the homeless, run into stiff political resistance in a permitting system designed to make it easy to block anything. That residents and voters seem to care more about what makes them feel compassionate than what demonstrably helps also helps little. The result is a mess.