It's definitely a thing. SF has a pretty substantial homeless population and apparently very few options for them to defecate that isn't the sidewalk. You can spend all day walking around playing human or dog. Walking by one of the BART stops on a warm day, you're hit with a pretty strong smell of urine.
Then you happened to avoid the places in those cities where people defecate. Trust me, it's a thing. Though it surprises me that even SF has this problem
If you're thinking of the same thing I am, then it's different. In some places, the only option may be to defecate on the side of the street by the curb, but that area gets swept frequently. I have never been able to play a dog vs human sidewalk poo guessing game as suggested above, including in the African, Asian and LatAm slums.
Perhaps it's because those people are not a transient homeless population that (presumably) gets cleaned up after, but they actually live there.
