I think that a big cause is that organized religion necessitates a respect for authority - specifically a respect for authority being able to provide factual information. Before everyone got all their information from Wikipedia, much of your information about the world came from school, or from church. However, now that information is available at everyone's fingertips, everything is fact-checked. When your pastor says that man was made in a day by God, then any smart-alec with a smart phone can turn around and say "well, science says it was over billions of years so..."

In short, it's a rise in skepticism. People argue that this is the same as cynicism, but I think it's entirely neutral. It's a normal human instinct to look for knowledge and investigate claims, and we can do that totally unfettered now, and many peoples' search for facts fills the gaps that God used to fill. In addition, we can find at an instant the errors, the inconsistencies, and the morally questionable truths about religions - and not just the one we grew up in, but ALL religions.

The people in this interview do a great job of describing many of the reasons - some lose faith because of difficulties, while others simply learn to question and find the facts that make faith unnecessary. Some still want to believe, but others are happy without God. I definitely approve of NPRs approach towards atheism and agnosticism as opposed to many mainstream media outlets who would have presented these people all as sad, hopeless, directionless, or belligerent individuals. I look forward to the day when we can turn on the TV or radio and see the nonreligious presented in this light.