Even lots of reporting isn't going to do much other than an LEO knocking on their door and asking them to please keep the dog away from the road.

No leash law is no leash law. You can't enforce a non-existent law just because a lot of people complain. Though some states have a provision for the animal to be removed for it's own good if it's a habitual problem.

The real problem is that people sit at home and see their dog ignore traffic, and think it's fine. Until that one time the dog runs out on the road. A good friend is a veterinarian and he says a near daily occurance is someone coming in with a badly injured dog and the same words every single time. "He/she has never run out in the road before!".