Oddly, we tend to think of rapists as impulsive, and bike thieves and muggers as somewhat rational economic actors. It takes minimal planning to steal a bike, and you're highly likely to get away with it, but mugging is a high-risk way to acquire money, and may be done somewhat on impulse. Comparatively, stranger rape takes planning.

IMO, if you can lurk in an alley for hours waiting for a distracted woman in impractical shoes to happen by alone, you have self control.