If you mean in-your-face, I'm thinking it's an urban density thing.
SF is small and incredibly dense. So, the homeless people that are there are packed into this tiny space along with everyone else and you literally have to step over them on the way to work.
If the population of SD was packed into the geographic area of SF with no available land to the North, East, and West, everyone would be stepping over homeless people on the way to work there too.
Same with LA. People come and jam themselves wherever they can fit. If there's fewer miles of sidewalk, density of homeless people goes up, it's more visible, and you get people living on your front doorstep.
On the list of urban density, SF is number 6 and SD doesn't even make the list.
https://en.wikipedia.org/wiki/List_of_United_States_cities_b...