A lot of bikes that are stolen are quickly abandoned and not everyone files a police report so they store them. And even people who had filed police reports will have often done it for an insurance claim and have a new bike by the time theirs is found, so it doesn’t get claimed . They do the same thing with seized and found cars

Don’t know about where you live, but if you report your bike stolen here, you get invited to the police bike auction and can get really nice bikes dirt cheap in a somewhat moralistic way

Earlier if you count Chechnya