Look at their methodology. They don't take into account the role of money in politics. Bribery of govt officials and politicians is legal in the US (they call it lobbying) so only the rich get to control politicians and their policies. Further, massive media conglomerates controlled by billionaires have an outsized influence on govt policy.

As such, while the US has the veneer of being democratic, it really isn't.

And I haven't even gotten into gerrymandering, which makes a complete mockery of democracy.