I agree that not every dog in this predicament has been purposely dumped. I’ve worked in rescue and sometimes you can piece together a story and sometimes not. I’m guessing that this one was treated badly and was afraid of human contact until it was very desperate.
I was watching a video about a mother cat having trouble because it had some kind of ring around its neck. It was easy to tell it was some kind of plumbing apparatus. The rescuers were able to follow the cat to a place with a bunch of abandoned sinks. She had put her head down the drain to look for food, got stuck, and forced her way out complete with sink flange. She’s lucky to not have been hopelessly stuck and died. In trapping her to attempt to remove the flange, she managed to remove it against the cage walls. They took her and her six kittens to the vet and got her some treatment. The flange had made it tough for her to swallow food and she had made herself weak by making sure the kittens were able to feed fully from what milk she could produce.