Propane bottle exchange, a target for thieves?

Everyone is talking about the 20 pound tanks here. But those of us who have 30 pound tanks don't exchange them. We get them refilled. If we in the 30 pound group can do it, I don't see why the 20 pound group has such a difficult time finding locations to refille and instead opt to exchange? I guess its a matter of convenience rather than necessity. Necessity MAKES you find somewhere to refill.