First, Japan's lower incidence of homeless is an anomaly mostly owing to the countries culture of extreme personal responsibility. If you've ever been to Japan you'd notice that extends to basically everything they do in public. Changing the culture of a melting pot of 300 million people is significantly harder than reading a wikipedia page. Side note (as someone whose been to Japan several times, and has several close friends who are Japanese citizens) Japan's homelessness problem is much more extreme in severity than raw number would lead you to believe. They have a smaller incidence, and the homeless themselves tend to try very hard to stay out of the way, but in the words of a Japanese friend "Japanese homeless are
very very homeless". They aren't just people down on their luck, they are people with extreme mental and developmental impairments. Japan has an altogether different problem when it comes to homeless than other nations, not to mention many non-profits think the government's official numbers underreport the population of homeless by 2-3x.(TL;DR: Japan is a really awful model for any other country to follow.)
Second, the US has a lower incidence of homeless people than many countries with much more generous social programs (Canada, France, UK, New Zealand). Saying we just aren't throwing enough of our wealth at the problem is also evidently wrong. (You can look that up on Wikipedia)
Third, the homeless rate in the US has been on the decline for decades. So blowing San Francisco's problems up into some larger conversation that the US as a whole is failing is just inaccurate.
Second, the US has a lower incidence of homeless people than many countries with much more generous social programs (Canada, France, UK, New Zealand). Saying we just aren't throwing enough of our wealth at the problem is also evidently wrong. (You can look that up on Wikipedia)
Third, the homeless rate in the US has been on the decline for decades. So blowing San Francisco's problems up into some larger conversation that the US as a whole is failing is just inaccurate.