Roto leagues are a COMPLETELY different kind of format, and my guess is, people like the divisional/playoff format for fantasy football, because that is what the NFL uses. It's more fun to mimic the NFL in fantasy football. In a roto league, head-to-head matchups don't exist, and the only thing that is important is the end of the year stat total. Some people like that type of format, but for me, I prefer the divisional, head-to-head format, because it feels more like an NFL schedule. To each their own, and each format has it's own positives and negatives.