I'm just going to go ahead and give a reminder that these statistics only represent correlation, not causality.

My guess is that it's more that when you don't have things, the more you tend to have more of a motivation to seek religion. That being said, it would be an interesting study to find if there was a causal relationship between non religiousity and certain markers of prosperity. As a "practicing" Christian, I'd honestly love to know, regardless of what the results are.