Dogs in rural areas are often abandoned there by people who somehow think it's kinder than rehoming them properly. If those dogs aren't taken to a shelter, or taken in (and they can't all be taken in), they usually die of exposure, sad and confused.

But random strays in urban and suburban areas generally just got loose. Though a random stray in a dog park, like, inside the gates, does suggest abandonment. (And even "just got loose" dogs can be abandoned if the owners don't care to pick them up.)