I don’t see it discussed in this article. But I recall reading another article suggesting that US Christianity is becoming more fundamentalist, which has been a driving force in pushing many people out, while leaving those that remain more extreme. The net effect is that while Christianity is shrinking, fundamentalism is growing. Coupled with fundamentalism becoming an increasingly political movement [0], and you see the current US.
Being Jewish, I’ve noticed a similar thing. Overall, people I grew up with have mostly shifted away from the religion (although still tend to consider them Jewish as a cultural marker). But those who are still actuvely religious tend to be more religious then their parents are.
[0] In the sense of governmental electoral politics.
