Many of the dogs have collars, so they aren't stray, but their owners don't bother tying them up. Almost nobody leashed his dog when taking Fido for a walk. Dogs sleep all over the sidewalk and in the streets, typically in parking places, usually placing their noses about 9 inches from traffic before drowsing off. I imagine that some of these sleeping dogs on the pavement are guard dogs owned by nearby shopkeepers, but there isn't all that much street crime in Turkey, so the dogs have it easy.
This sounds fairly chaotic, especially with cats everywhere, and many of the dogs with lean and hungry looks. Yet, it isn't, because the dogs, about one-third of whom appear to be some kind of retriever, halfway between Labrador and Golden retrievers, are so laid-back. I saw a dog curled up dozing with a sleeping cat, like a picture out of a children's book. Other times, I saw dogs sleeping on the beach a few feet from sleeping flocks of ducks and geese. Most of the few yappy, hyper dogs in Turkey were held on leashes by German tourists.
The reason for the profusion of dogs in Turkey is presumably the lack of programs for and indoctrination into neutering dogs. As my son pointed out, to enjoy a well-run country like Sweden, you have to worry about a whole lot of little niggling details, like spaying dogs, that most people in the world just don't worry about.
As for the personality differences between Turkish and American dogs, I can only speculate. My guess would be that in a society without much in the way of leash laws or big backyards, dogs with anti-social habits are dealt with, summarily, and that selects for pro-social habits of sedateness among the survivors.