My theory is the number of people in a city willing to commit bike theft is finite, and more bikes in public isn't going to draw out very many more thieves out of the woodwork since bikes are already easy to quickly find to steal in public. That means if the world changes and you get everyone biking, rate of bike theft drops down low enough where its something most people don't think of, like how grand theft auto is an extremely rare occurrence despite there being plenty of expensive cars parked on the street.
