The amount of money they make from real multiboxers may be negligible but the amount they make from people with more than 1 account is very substantial. It would not be easy to disallow boxing and still allow multiple accounts. That is the reason we are "tolerated" in carebear MMO's where the majority of the population would enjoy having us tossed out.

The GM response from EvE was far more tactful when they explained how multiboxing was explicitly allowed.