San Diego does have quite a lot of homeless, but it isn't as concentrated geographically.
I'd argue that part of the issue with San Francisco is the concentration of the homeless into a small area. You don't see homeless in Atherton, for example. The wealthy enclaves in the Bay Area have zero problem with pushing the homeless out of their areas into somewhere else. In the Bay Area, there aren't that many "somewhere else" left so the ones that remain get overloaded.
I'd argue that part of the issue with San Francisco is the concentration of the homeless into a small area. You don't see homeless in Atherton, for example. The wealthy enclaves in the Bay Area have zero problem with pushing the homeless out of their areas into somewhere else. In the Bay Area, there aren't that many "somewhere else" left so the ones that remain get overloaded.