I don't know if the OP has just been lucky enough to be places where they weren't robbed but I know it does happen.
I think every campground is different with different inhabitants, both long term residents and weekenders. All we can do is be proactive and not temp anyone who might decide they want to steal something.
We do put away our loose items if we've been sitting out, not just to prevent theft but to keep the campsite neat and to keep the wind from blowing stuff away.
Therefore it has to be everyone personal choice.