I have been running a dashcam in my car for 15 years now. My first dashcam was an original X10 camera hooked up to a VCR that I had to hit record on every time I started the car. After that I used a home CCTV DVR, then a AverDigi 1304MOB. Got into the HD dashcam scene very early on.
My opinion is the slow US adoption comes from people either not knowing the risk or thinking installation is too complex/expensive.
From a risk perspective, when I tell people my first dashcam was installed after I lost an accident case due to the other driver lying to the police. Almost everyone has a story of something similar, yet they still think a dashcam is too much.
I was in an accident a couple of weeks ago now where a pickup changed lanes into me. The insurance adjuster on my side told me that they see video in only 1-2% of cases (more than I thought!) but most of that is either the insurance company's own "Teen Safe Driver" program that hands out DriveCams, or CCTV/red light cameras etc. Very, very few private dashcams. After showing my video to friends at work, 2 of them ordered 0805s right away.
My wife never wanted a dashcam in her car until she got in a disputed accident and was blamed despite her protests. Now she has a GS9000.
There are occasional stories on the new where a dashcam caught a clip, but i find a lot of my friends share the "You must be hoping for an accident" view. Having said that, they don't agree that my home CCTV indicates a desire to be burglarized, so...?
Back in the day my dashcam was quite an overhead, but now it just plugs into the cig lighter and I forget about it. For under $100 and a 5 minute install I simply cannot understand why anyone would NOT want one.