In my state, gravel is the new pavement. If you want to get away from heavy traffic, your choices are bike paths or minor roads that are crumbling. Some counties are converting pavement to gravel because it's cheaper to maintain.
So far as bikes go, I think it's hard to guess why certain bike categories are popular, because a lot of casual users such as myself aren't committed to riding under a limited set of conditions. We're looking for something that's likely to be comfortable, versatile, and that looks good.