looking at the chart, it's obviously something changed in 2000. all the other countries in the study started going down and the US started going up and both trends continued for 20 years.
one thing that automatically puts the US at a disadvantage to the other countries in the study is our population is much higher, spread among a wide diversity of rural/urban and racial backgrounds, so putting any one change into place that may mean a lot in Italy or Ireland will have less immediate impact in the US.