I'm no expert in this area, but I think it is partly the sexualization of the media. Sex sells. And once you look at porn even once, its progressively addictive. I know of a site that addresses these issues if you are interested PM me. It's a Christian site, but it is not in the least preachy. In fact the only thing that appears to make it Christian is the name.

They have a discussion board (which I would marginally recommend. They aren't that great IMO, and they have lots of "confessions" from people struggling with porn and sex addiction, all speaking very candidly and openly.