I live in the USA. I can't even say that there is such a thing as "the American church."
I am 76 years old and have never belonged to any church. But even as an outsider, I can see, just by walking down the street, that there are many, many churches, many denominations, many different churches.
To lump them all together as one does not seem realistic.
All I can say is that if these churches are losing membership, it must mean that people, in general, are starting to think for themselves and not believing the fairy tales that are taught in churches.