The Chickenboners and the Lumber Cartel are waging a war over your email box. That doesn't sound much different than direct snail mail advertising, and it's certainly cheaper. So the business pays the spammer, and gets a mailbox full of complaints in return.
Spammers are also into pyramid scams.
They are like mosquitoes in a swamp. If there is water to breed in and people from whom to suck blood, they will survive. Spam-fighters say the best action for individuals is to identify the source of the spam. Then contact the abuse desk at the Internet service provider where the spammer has an account and ask them to terminate the service. But spammers are onto this technique and typically supply false email addresses or ISP information in their mailings.