I wouldn't be surprised if increasing numbers of SUVs and pickup trucks in the US is at least partly to blame for this. If you're hit by a sedan, you're likely to get thrown onto the hood, windshield, or roof of the car. If you're hit by an SUV or truck, you're much more likely to get dragged underneath, where you can get run over by the wheels. While neither situation is particularly fun, the latter is much more likely to result in death.
> The other obvious difference is the huge, multi-lane roads in America, sometimes with no sidewalk.
It would also be interesting to be able to classify what was happening when the pedestrian died in data like this. Were they crossing the street and a car going perpendicular ran into them? Were they crossing the street, and a car turning from the parallel street ran into them? Or were they walking along a road without a sidewalk, and a passing car hit them?
Agreed that the US has a lot of wide, multi-lane roads, and poor sidewalk coverage on many roads, but I don't expect that situation has changed (for worse or better) all that much in the past few years, in a way that would explain the surge of fatalities.
But anyway, to explain the increase in fatalities, my money would be on smartphones: more people driving distracted, and more pedestrians walking around buried in their phones, having no idea what's going on around them. Another posters somewhere here pointed out that pedestrian fatalities have been rising steadily since their all-time low back in 2009, which roughly coincides with the rise of smartphone adoption.