Here in Santa Cruz where meth and heroin are big issues, bikes are a sort of "currency". Most bikes when stolen are mostly parted out and the scrap metal sold or parts sold -- this is at the low to mid-range. For hire end bikes, they are often collected and shipped out of the city (and often times state/country).

While I do a lot to advocate for registering bikes here in town (a group of volunteers I am part of has registered about 300 bikes), the reality is registering doesn't dissuade anything. Here, it gives the cops a tool in case they do find one of the local tweakers with another persons bike.

Yeah in Santa Cruz a stolen bike lasts about 15 minutes before it's parted out to a stolen frame, stolen wheel set, stolen handlebars, etc. Probably similar in other places.

So while you might get your frame back, you can kiss everything else goodbye. It's better to be smart about where you leave your bike and how you lock it.