Just silently mass banning does little. They did some banning in Mabar, people barely remember it or just vaguely heard about it.
DDO is a small niche product with a small player base, they can't afford to lose paying customers. If exploiters are F2P it won't hurt them. But if they ban customers who spent alot of money, its going to hurt DDO more than the customer. People move on to do other things. DDO lost a paying customer and a player.