Oh really? Mine is usually in my garage,* but in the wild, I always lock it. I carry too many tools in the trunk, other things in the console and glovebox, along with my car insurance, etc. none of which would I carry in a rental while on a trip.
* I'm the only person I know who backs into his garage. It makes loading and unloading easier like after grocery shopping or before tomorrow's road trip, but I do it mostly so I can watch for neighborhood children, but then here they play in the street as well.