I actually worked a bunch of carjackings back in the 90s when they were big news and were made a federal offense.
Not a single one happened by a thug walking up to an occupied car. Even criminals realize there are guns in there, and also all you need to do is hit that long skinny pedal on the right and off you go.
All the ones I worked happened as a driver approached the car. Then its gun in the face, keys please, and there goes your car and your gun strapped to the steering column.
One of my buddies got carjacked (almost) as he and his pregnant wife walked up to their car at their DC apartment complex. The guy with the gun got the key, got into the car, and then used his gun hand to go from PARK to DRIVE. As soon as the gun was off him, my pal drew his issued 226 and let fly. He shot the bejeebus out of his own car and ventilated the 19 year-old-used-to-be-carjacker, who he pulled out of the car and sat with until he died.
I know there are carjackings where someone runs up to your car while you sit there with your foot on the gas and your hand on your new Governor, but in my experience they aren't the norm.
One of our brethren darn near ascended to heaven after he contacted a person who matched the description of one of two carjackers (CA Penal Code Section 215). They had murdered a young mother during the attempted carjacking. The suspects were male, black, mid-20's. They were out of LA. My good friend and our brother cop was black. He told me the description didn't quite match. As soon as he took his hand off of his gun, the suspect drew his and shot our brother cop approx an inch below his vest. That round did flat line him. Surgeons saved his life.
The point is the uninitiated must never underestimate the danger that carjackings present. A bad guy can have all I have except the lives of my family and my life. If bad guys drive away in my ride, I'm good as long as lead didn't fly. Insurance will buy another car for me. The dead are never resurrected. And cops will catch the bad guys.
I'm very lucky to live in an extremely safe city. 90% of the time, I'm merely retired and living happily. I can't tell you the last time I've had a gun on me even though I have retirement credentials that are good in CA and HR 218.
Knowledge ingrained is never purged. What might appear innocuous to the uninitiated might be potentially deadly actions to trained professionals. Two dudes walking into a store with a third standing outside of a running car that's parked close to a shopping center exit might be conspiracy to commit armed robbery. If a cop is going to fire his duty weapon, armed robbery is the call most likely to require deadly force. Armed robbers are predisposed to commit murder.
I'll never initiate contact. I'm retired. I don't have to do a darn thing. Avoidance is the only known way of assuring that I'll remain vertical. Cops don't have such luxury. They have to contact bad guys who'll kill 'em if they get a chance. Cops in urban areas have luxury of responding en force thereby telling bad guys that resistance is futile. The law, not they will win. 10 cops at a car stop are conveying the palpable message to those inside the car that should the decide to opt for stupid instead of following the program, they will not win. If you see a lot of cops at a car stop, it's safe to assume that they have knowledge that the public doesn't.
Bad guys know that if they attempt to murder a cop or murder a cop, any cop: constable, game warden, city, county, state, federal and manage to escape, every cop in the country will be hunting them. There are probably at least 30,000 city, county, state, and federal cops in LA County, maybe closer to 50,000. If a bad guy harms (or worse) a cop in a no-stop-light town in the deep south and seeks refuge from his homey bangers in LA, every cop in LA County will hunt him down.