Spammers pay large amounts of money to have their millions of mostly unreadable spams sent out. So what’s the payoff to them, especially considering the risk?
I believe the leaders of the gangs you can hire to do spam runs are in it for the money. But the people paying them for most of the spam runs have some mental disorder. There’s nothing rational about it. And the spammers-for-hire know it and exploit the illness.