"Bike thievery is essentially a risk-free crime"

... and is lower in places ... where lots of people have bikes already

I don't have the stats, but massively doubt this. Bike theft is high in cambridge and amsterdam. there used to be a story (in cambridge) that vans would come from out of town, drive round in the middle of the night, cutting locks and stealing bikes to take down to london or sell on elsewhere. a lot of people leave their bikes on the street over night and use flimsy locks.