Your question probably has an answer in the form of many companies past and present attempting to do exactly what you say "disrupt". As pgt mentions, the gamifi

Your question probably has an answer in the form of many companies past and present attempting to do exactly what you say "disrupt". As pgt mentions, the gamification is 1 of the biggest factors in play here. Buyers will go by ratings based on other buyers and sellers with massive amounts of positive ratings have little incentive to build rep again.