Part of this problem is caused by automobile manufacturers designing vehicle doors to unlock automatically when the driver unlocks and opens his/her door. Even if the driver locks the doors after exiting, there is still a window of opportunity for thievery.
Same in a parking lot. When the driver’s side door is unlocked, all other doors automatically unlock, and during that moment, the driver is vulnerable. Anyone can hop into the back seat while the person is entering, or exiting their auto. Not all motor vehicles have this design flaw.