I'm not sure. They may well consider human safety.... Well, at least their own safety.
Usually they leave my $1 lights alone.... But, I've even had the $1 lights stolen.
I've thought about this recently. If the states, cities, and the police really wanted to be pro-cycling, they'd make it a felony with at least 30 days mandatory jail time to steal a bicycle, or remove anything off of another person's bike including critical safety equipment. They might get a surge of arrests, but then the entire cycling community would become cleaner very quickly.
I wonder if you could even file a police report for stolen $5 bicycle lights. But, if people were going around stealing car lights, the newspapers and police would be right on top of it.
Stores (and communities) should be encouraged to not only install bike racks, but also to have surveillance of those racks in high resolution and multiple angles, as well as easy access to the data.