Apparently spam has become incredibly organised and is increasing dramatically. But here's an observation I can buy in to:
It is difficult to fight spam because the problem crosses international borders, said a spokesperson for the UK Information Commissioner's Office, the body which enforces the law.

Some believe laws and filters won't defeat spam.

It will only end when people stop buying diet pills, herbal highs and sexual performance enhancers, said Dave Rand, of Internet security firm Trend Micro.

"The products they are selling by spam are exactly the same products that they sold in the Middle Ages," he said. "This really is a human problem, not a computer problem."
from M&G article here