It takes a very low percentage, usually well below 1% to make the effort pay off for these scams, and the spam sales ones. These industries (along with gold sellers in games) continue to evolve to drive down cost while trying to keep their market reach for their message as big as possible. It's much like the evolution of other businesses over time, just with some illegal actions added in.

I deeply respect the people out there who try and combat this mess. It's a very tough issue to solve.