IME, and as the article also kind of says: paper mills target academics from developing countries. Academics who have trouble competing because of lack of funds, or lack of proper support from their universities, language barriers, cultural barriers, etc.

As you mention, being in academia is tough. Some people just can't compete, and then get lured into accepting offers like these. In a way, I think this is similar to how vulnerable government officials get bribed. It's not something you do unless you're rock bottom, and don't see anywhere else to go.