I remembered that someone on this forum had a gnarly story of a guy's PU truck running him over but I could not remember who it was. Now I know. It's amazing how quickly things can get away from you with a rolling vehicle that weighs a couple of tons or more.
I also don't understand why people don't use their parking brake. I use it almost always when any vehicle I'm driving is parked. Level ground...doesn't matter. I had an old childhood friend visiting me last year and I loaned him one of my cars, old Mercedes diesel. I'm giving him the 10 cent tour of the controls in the car and I show him the parking brake release. He asks me, "when do I use that?"
"Every time you park the car," I tell him. He's 65 years old and has been just throwing cars in "Park" and walking away for 50 years, even on slopes. I give him the whole lecture about how the parking prawl on an automatic transmission works, how a good driver engages the parking brake before letting the vehicle rest on the prawl, etc...
He's nodding but I know that he thinks I'm crazy or something. I ask him if when he parks on a hill, can he feel the car *bounce* on the transmission lock and does he notice that it feels like something is going to break when he takes it out of "Park?" He actually says that yes, he has noticed those things, it just never occurred to his unmechanical brain that he was doing anything wrong.
I'm a bit strict when it comes to the subject and I almost always use the PB when I park anything. The floor of my shop is so level that we can roll cars around and not even put them in gear or use the brake and they will not roll but anywhere outside, I use it. It's a good practice and your car or truck will never run you over.