Flagrantly flouting the law and thumbing their nose at the police eventually causes the police to come into disrepute if they consistently show they don't care about theft.

The police force can only really enforce the law because society gives them permission to do so. The instant that you have mobs of Bike Batmans the police will act because now you have increased vigilantism - and people taking the law into their own hands.

This sort of thing can escalate very quickly. If bike batman works well, then why not murderer batman, or rapist batman? And then there is the escalation of enforcement. What if bike batman decided to really get serious and use a gun to get the bike back?