Since this is a 20 year study, it would be intersesting to see if the change happens to people in the same age group (20s in 1990 vs 40s in 2010) or if the change comes from older religious people dying and younger non-religious people being brought up.
My parents took me to Sunday school when i was a kid but in 1945 when I was 8 I kicked religion for hot rods and drag racing and split early Sunday morning and never went to church again except when we got married in 1958.
As far as i’m concerned religion is nothing but a crutch for weak minded people and so much BS with just about as much relevance as Aesop's Fables.