You're making the mistake of assuming car thiefs are unintelligent or unorganized. Successful thefts that return a profit require a network of skilled people to pull off and talent can be found within that pool or recruited.
By saying a thief would have to understand how a computer exploit works, it's saying a thief needed the equivalence of an engineering degree to drive away with a car before computers entered the equation.
Exploit discovery, maybe, but it doesn't take much to execute packaged tools you bought on the blackmarket.
> while popular older cars are stolen in vast numbers
For now. Once they get out of circulation only newer cars will be left and at that time it might be that thieves could buy devices to hack into these cars just as you can rent botnets today.
By saying a thief would have to understand how a computer exploit works, it's saying a thief needed the equivalence of an engineering degree to drive away with a car before computers entered the equation. Exploit discovery, maybe, but it doesn't take much to execute packaged tools you bought on the blackmarket.