I remember when my grandparents had two German Shepherds, Rocky and Lucky, and they stayed outside on about 5 acres in Missouri. But it was outside of county lines, and they had ponds and such. The dogs loved to roam freely and would come back home!! They would go over to the neighbor's and bark at the cows.
I think some times people who are out in the country, don't realize they are subject to city ordinances. If they live "out in the county" and not in the city, the leash laws may be different. I had this problem when I lived in a small town in Kansas near Kansas City. There were city ordinances and leash laws, but the neighbors with their pets acted like they lived out in the county. They did that with fire works, too. Didn't realize they lived in a denser area than out in the county.
I can't tell you why people do this, except, as someone else said, people break laws all the time and don't even think about them. If they are not enforced, even MORE people break laws, and at the same time, under funded police departments have bigger fish to fry than dealing with off-leash dogs.
I DON'T live in the city. I live at the edge of the suburbs in a town that is zone residental/agricultural except for a small business district. I have a 5+ acre horse farm and back up to another much larger farm, and have wooded town-owned land to one side. We STILL have trouble with loose dogs, and it's not OK here, either.
I HATE going out and stepping in huge elephant plop sized dog poop in my yard that CLEARLY didn't come out of Kodi. (besides, we pick his up when he goes) We once had a neighbor's Rottweiler cross who would come and run our horses. When I yelled at him when I was out doing stalls one day, he came after ME. Fortunately, I had a pitch fork in my hands, and he actually bounced off the tines before he retreated. Otherwise, I'm sure he would have attacked me. We have another neighbor with two Springer Spaniels. These are both nice "people" dogs, but one of them is very dog aggressive. I have to walk right by their house to get down my driveway, and twice the dog has come running out and tried to grab Kodi. I've had to yank him up off the ground with the leash, then kick the dog off repeatedly before the owner came and dragged him away. They apologize profusely, but they don't maintain their fences, and don't properly supervise their pets.
Another time I was carrying groceries to my house from the car. Kodi was off leash, as he often is in our yard, following me back and forth as I brought the groceries in. (our yard is set WAY back from the street at the end of a very long driveway, and is out of line of site of these dogs) The dog came charging INTO our yard and grabbed Kodi ON OUR BACK STEPS. fortunately, because of Kodi's long coat, he only got a mouthful of hair for the effort before I chased him off and got Kodi in the house.
People seem to feel that because there is open land (ours) behind their house, it is fine to let their dogs run loose. But it's MY property, and I want to be able to SAFELY use it for my own animals. So this is not just a "city" problem.
Around town, people do, for the most part keep their dogs on leashes, and MOST people (besides my stupid neighbors) either have solid fences or "Invisible Fences". But they don't clean up after their dogs on the street... Walking down the sidewalk between our house and town is like walking though a minefield.
So, I don't have any answers for you, but I'm right up on the soap box with you. These people are irresponsible and a danger not only to other people's pets but to their own as well.