I think what many of you are missing.
You break a window it makes a noise, sets off an alarm and it is obvious from the get-go that the car is being broken into.
If they unlock the car and are smart, there is not much to say they are not the owner until they are running away. Specially if the alarm thinks it was mechanically unlocked with a key. This gives them more time to do a thorough job and also makes them much less likely to be caught or confronted.
If you break a window, it doesnt set off an alarm.
Only till you open up a door does an alarm sound.