There's a few problems with your theories, like the fact that in most places, every door has the holes drilled in it for the hook, but many have no hook. Did the purse snatchers do the drill work, but forget to bring enough hooks? You know, the drills used to put hooks in metal doors make a fair bit of noise, did no employees of these "nice" places notice the work going on in the loo?

As one person in this thread pointed out, some people actually use these hooks for coats! I guess that's an unintended public benefit from the purse snatchers' decision to install hooks in stalls.