[sewercake]

It's interesting, many people in this comment section are pointing out other places, like greece, the caspian sea, the black sea, where cats are found all over the urban environment. What all of these places share (including istanbul) is their proximity to water, and presumably, ports! When I was in istanbul, I remember someone saying that the cats, historically, would help tame the massive rat populations that often plague both port cities and the hulls of ships. I don't have a source to back this up, but its some food for thought!

[reducesuffering]

Not exactly. No US cities have the abundance of stray cats roaming around, even though LA, SF, NYC, Boston, etc. are all up against the water and ports. Elsewhere outside the US, Tbilisi, Georgia isn't very close to the sea and yet it's also filled with stray cats and dogs.