Eh it's CNN. Always wanting to try to create controversy for things that don't exist. Well sort of.
I don't need to read it but there's a few reasons why you will find a larger population becoming irreligious, but I wouldn't necessarily say atheism.
Protestantism in America, I strongly feel, is losing its grip and it's power. And it doesn't have the foundation to withstand some of the prevailing problems such as moral relativism.
I think it's easier to believe God doesn't exist now than it ever has before.