Bit of a difference from harsh punishment not deterring theft of something you need to live vs. theft of something like a bike. When the punishments for stealing anything at all are as severe as hanging, exile, or losing a hand, do you really expect much else besides necessities to be stolen? I suppose you still might expect all sorts of things to be stolen if the chance of getting caught is nil, as it is with bikes -- you still need a strong enough probability of getting caught to back up whatever punishment is decreed, which is why bait bikes can be a helpful tool. I doubt better locks would work, I remembered this video from years ago on how even ridiculous methods of stealing a bike won't get much attention: https://www.youtube.com/watch?v=ZbklkFuFk-4 (And if they did, a thief can probably convince most people it's their own bike and they lost the key/combo -- I kind of suspect that possibility goes through the minds of onlookers anyway.)

Some punishment at all might be useful, though. Instead of none at all.