Our stores are full to bursting with BSOs. A lot of folk are too idle to take them to a scrap dealer themselves, and it's now very difficult to legitimately sell scrap. We have literally hundreds of old bikes a year handed in as "found abandoned" bikes, which are very, very rarely claimed. Your average Joe cannot tell a decent bike from a rusting heap of abandoned crap, and so we get them handed in all the time. All the found bikes are sorted on a two monthly basis by a recycling project. They cannibalise any usable parts, and take away stuff that can be repaired and passed on to folk that need them. No-hopers are scrapped, and anything half-decent is sent to auction.
We get very few reports of stolen bikes, and those that are reported tend to be high end stuff anyway. When they are stolen owners tend to be able to describe them in detail
The few people who bother reporting bikes stolen from gardens tend to describe them as "Boys MTB, blue" with insufficient detail to match any of the hundreds of bikes "found", so recovery is unlikely. In this throwaway society a lot of people leave them out in gardens knowing that travelling scrap dealers will come and collect them and save them the bother of getting rid.
Looking at the pile in the photo, I would say there isn't a decent bike amongst them. If you say you saw a Giant Susser on the back, did you note what sort it was? Was it in decent fettle? Your alarm bells and Spidey Senses may have spotted the one decent bike that has been lifted in the process. Who did you tell?