Is it the case that the folks with a big spam problem are not using efficient filters, or ISPs with efficient filters?
As for why it is profitable for the spammers, there are plenty of naive consumers in the world, as well as (apparently) incredibly generous people who love to help out Nigerian officials' widows. The telemarketing business is also going great guns, AFAIK, even with "no-call" lists.
Jon Johanning // jjohanning at igc.org __________________________ The mass of man[sic]kind is divided into two classes, the Sancho Panzas who have a sense for reality, but no ideals, and the Don Quixotes with a sense for ideals, but mad. -- George Santayana (Interpretations of Poetry and Religion)