Not all thieves will break a window, especially if it's in daylight in an open parking lot / or street parking, more likely they might just go around looking for unlocked cars especially in places where people tend to run errands mid day in which case they might leave the car unlocked if they only pop out for 5min.

A guy taking something out of the back/front seat isn't as suspicious as some on going around with a crawbar smashing windows.

I've seen individuals going around a parking lot actively looking for unlocked cars couple of times in my life usually a blow of a horn scares them off.