I'm not so sure about that. Have you ever played fantasy baseball? Or fantasy hockey? Most other fantasy sports are a pain in the butt. They're too involved.
Fantasy football has a nice rhythm: Peak at your team on Thursdays half-way through the season because of the handful of Thursday night games, adjust your team at lunch on Friday, check your scores on Monday.
At least for casual people. Maybe those hard-core will move to fantasy golf...