Personally, I think it is a matter of what is deemed valuable by the thief rather than the owner of the vehicle. My best friend has had her car broken into three times & there was never anything of real value inside - at least to her. The three times her window was broken out the only items stolen were things like a jacket, a yoga mat, blankets, and pennies - yes, pennies, as in less than 15 cents in pennies in her ashtray.
I sort of wonder if some of the really desperate homeless people did it. While a yoga mat, blankets, clothing & pennies don't seem to be valuable to most, maybe they are very much needed & valuable to those who live on the street. So my best friend does not lock her car doors anymore since she can't afford a fourth window to be replaced, & she has yet to have anything taken from her now unlocked car.