Interesting. I'd make a guess. In a cat friendly city like Istanbul you'd see cats freely and safely venturing everywhere. Rats would have no chances say in a cafe where a couple cats are sunbathing. Where is in cat unfriendly cities like a typical American city the cats aren't present on the streets, probably because this is where they get caught by Animal Control, etc., and they are more confined to some back alleys, empty lots, etc. And the rats problem for example in NYC is a street problem, i.e. where the trash is. And for example here in Bay Area the several colonies of feral cats that i know about aren't in populated areas where they could have been impactful upon street rat/mice population, instead these colonies are pushed out onto the edges of wildlife areas (where they still do useful things like protecting the birds nests/eggs from rats, etc., yet it woudln't really affect rats in the populated areas)