After a few months, the damage has already happened. The botters don't give a damn if their accounts are banned since they already have had months worth of time to grab cash from buyers.
I'm not talking about individual botters, they get what they deserve but the gil/shard/whatever sellers will be back the next day setting up their bots again. They get reported again and S-E takes action after a few months. This get's repeated over and over. Mass banning does nothing against rmt botters.