This looks like a curve that was drawn by hand, rather than fit by least-squares, but there is obviously a correlation: as a country gets wealthier, it gets less religious. The United States, obviously, is a whopping outlier. Why is that? What is it about the U.S. that makes it so different from our demographic cousins, even within the Anglosphere? (Kuwait is also an outlier, but the reasons are pretty straightforward.) I’ve heard various theories, but none has really been convincing.
(Looking closely, maybe a better fit to the data would be to horizontal line segments: one at 2.25, for GDP between 0 an 10,000, and one at 0.75, for all higher incomes. Perhaps there is a phase transition that countries undergo when their per capita GDP hits around 10,000. Or, even more likely, there is some hidden third variable that is highly correlated with both GDP and religiosity. That kind of curve would make the U.S. seem less exceptional.)