Or is it?
A study by Stanley Presser of the University of Maryland and Mark Chaves of Duke University has found that that religious attendance did decline slightly between 1950 and 1990. Especially among the Mainline Protestants and post-Vatican II Catholics.
But evidence from several sources converges on the same answer: weekly attendance at religious services has been stable since 1990 at about 25%.
Why is the US an exception? Or should we be asking, Why is Europe the exception?