One thing they look at is life expectancy and the US ranks 35th in that area. The problem is the US has had increasing economic inequality over the past 30-35 years (economic inequality in America is now worse than that in the UK and worse than that of several Latin American countries) and America's overall numbers are dragged down by having more poor people than a country like Sweden.
the only reason that USA is lower on the list is quite frankly due to the large Black and Hispanic population...they just drag USA down....
If you just count the white and asian life expectancy...then USA is right up there in the top 10