That's complete bullshit. The reason is 100% because of the economy. Many of them will say it's not, others will also believe it, but if you dig down to the truth, it's absolutely and exclusively all about the economy.
> Robert Wuthnow, a sociologist at Princeton University, spent eight years interviewing Americans in small towns across the country.
Now, that isn't peer-reviewed research, and it doesn't necessarily prove anything, but it's a decent start toward being authoritative (even if I find it quite unconvincing).