People switched from Digg to Reddit for mainly two reasons. 1. Digg started sucking 2. Reddit offered a truly innovative feature that most people found useful

People switched from Digg to Reddit for mainly two reasons. 1. Digg started sucking 2. Reddit offered a truly innovative feature that most people found useful, subreddits Reddit is still great, and this doesn't offer any significant features that I'd consider important enough for most people to switch.