Sometimes they get dumped for no reason other than whoever had it couldn't be arsed with them anymore. Or they've gotten lost with no identification, or left behind when the cops have turned up. I've seen some blinding dogs go through rescue, makes you wonder why folks would put so much time and effort into them and then let them go. Young dogs or older, if you know dogs you can pretty much get a feel for weather a dog will be what you're looking for; put in a bit of effort you'll often get it back 10 fold. It certainly wouldn't hurt to have a nosey round, see what's out there.