Having spent some time in academia I can tell you the answer - it's the cheating. The rise of science in developing and recently-developed countries where corruption is still endemic has led to there being a large cohort of students and "scientists' who think it's ok to cheat. This is a cultural thing - they're not bad people, and often not even bad scientists - they're just used to a society that operates like this. Don't take my word for it - look at the article and we see the following:
> Jack Ben, of a firm whose Chinese name translates to Olive Academic
> researcher and assistant professor in Saudi Arabia, Malaysia, and Jordan.
> the company acts as a broker, sharing payments from the paper mills with multiple editors—including Omar Cheikhrouhou of Taif University in Saudi Arabia and the University of Sfax in Tunisia.
> A Ukrainian paper mill dubbed Tanu.pro
> While he was visiting his parents in India last summer, a Dr. Sarath of iTrilon reached out to him on WhatsApp, offering authorship of “readymade papers” with “100% Acceptance Guarantee.”
> in Russia and several ex-Soviet countries, for example, policies focused on publication metrics, coupled with a culture of corruption and the transition to market economy
This culture is slowly corrupting scientific journaling itself as an undertaking, firstly because established journals will end up employing some of these people (as in the article), but more importantly because as mentioned, it's a culture problem and who doesn't want easy money and guaranteed quid-pro-quo publication when all your friends are doing it? After all, you're not a bad person and I'm sure your science is fine.