Really a cost/benefit thing. Yes, it does make it harder, but not really so much harder that it's going to keep a significant number of people out. If they we

Really a cost/benefit thing. Yes, it does make it harder, but not really so much harder that it's going to keep a significant number of people out. If they were more popular in practice, more people would learn to pick them. They also make the lock more prone to jam, and not as smooth.