Users have to install a browser extension in order to participate in the study. That's a way higher barrier than the personality quizzes that Cambridge Analytica used.

It also happens at a different layer of abstraction. Cambridge Analytica extracted data through the permissions framework that Facebook itself implemented.

Facebook's interest in its users' data doesn't need further explanation after you see that most of their profits derive from their control over it. The same control that allowed the profitable mass political targeting that these researchers are trying to study.