With an Alexa rank of 380, I wouldn't dare to say that DMOZ is an out-of-date concept, I would compare them rather with the Boeing 747 than airships: large, long existent and with a history where no successful competitor apeared. The 747 is flying commercial flights for 37 years and only since a few years there is a competitor starting to penetrate the market, the Airbus A380.
Boeing had a critical mass in the market of large airplanes with the 747 and reaching that critical mass is a difficult task (and in airplane industry really expensive) for competitors. Once there is confidence in a concept, why change to a comparable concent that hasn't proven itself? Airlines were happy with the 747, why switch to another? Volunteer editors (and looking at the Alexa rank, users also) are confident with DMOZ, why switch?