I think its also where the new transplants end up. They end up in the recently gentrified areas such as the Mission/Castro/Dolores due to affordability/closenes

I think its also where the new transplants end up. They end up in the recently gentrified areas such as the Mission/Castro/Dolores due to affordability/closeness to the GBUS, etc. Being fairly adjacent to the Tenderloin/City Hall/Haight, people are generally going to have the guard up higher and you'll have more interaction with the folks who've been gentrified out. YMMV but if the author was in the more residential areas such as Marina/Cow Hollow/Inner Sunset/Noe Valley and jogged the same routes regularly, perhaps he'd have had a more small town interactions.