Dan, I'm thinking that part if is because things like school/theater/etc shootings are becoming more common and so the mindset has changed. We're long past the days where there might be a troublemaker or two in town that got hauled in every weekend when he got drunk or whatever. Society is more violent and more socially connected, so we all hear about these incidents.
I personally know of several situations where cops stopped someone for a traffic issue and were either shot, stabbed, or beaten. I know a cop who is now in a wheelchair for life because he chose the kinder, gentler approach and got shot for it. My sister's ex knocked on a door to serve a warrant and was shot, beaten, and held hostage. I suspect it's this stuff that causes cops to shoot first and ask questions later when their lives are on the line. I can't blame them, and I wonder what systemic changes can be implemented to both protect cops and reduce police shootings. I'm not sure there's an answer.
Edited to add: I think another factor in this is the recent glorification of "thug life".
