Looks like a project bike to me. Was in the back of a car maybe and wife/girlfriend got sick of it being there when they got something new at one of the stores that the parking lot was for. Pitched it out, or maybe just forgot it after re-arranging stuff.
Maybe they didn't meant to leave it and just forgot to put it back in? Maybe instead of a bunch of items they bought they had a flat tire and had to take the project out to get at the spare -and then forgot to put it back in?
The possibilities are endless.
My money is on a project bike that was never finished looking at those brakes. Maybe it got stolen as is and then dumped later. Maybe someone just wanted the cranks?