I should add too that I know dog behaviour and body language, and I KNOW that a lot of these dogs, on top of what I said above, are also subject to anger and harsh punishment if not abuse by the people. I know human behaviour too, and it's not hard to spot someone who has come to really resent their dog. It is only natural to an extent, because for some people, it's the ultimate insult or sign of "F you" from a dog, to take their property and pee/poop on it. Even if the people can hide it, the dog tells all. A good trainer/behaviourist can tell a lot about what a dog has experienced and even often when he's experienced it, by his behaviour. I know that a lot of these dogs are viewed as ignorant spiteful jerks by their owners and they pay. It's so horribly tragic, because it is NOT THE DOG'S FAULT. It is HUMAN error. These dogs if they're lucky, make it to a trainer like me who knows what time it is and can reach the owners (believe me, it's a lot easier to deal with the dogs than the people. Many people are only interested in hearing what you have to say if you're telling them yes your dog is very bad, and you've made no mistakes! Many have zero interest in hearing that they've made a mistake, even when you take great pains to let them know you're not judging them). But most often, they end up in a shelter or pound and euthanized, gassed, or heartsticked. Or if their owners choose, to be brought to the vet and euthanized there.
The number one cause of death of dogs under 1.5 years of age is behavioural problems. This scenario is far, far too common, and is really serious stuff.