The incentive to freely review others' work is that others will also freely review your work. This is quite separate than the exploitative aspects of the big s

The incentive to freely review others' work is that others will also freely review your work. This is quite separate than the exploitative aspects of the big scientific publishers. Reviewers are certainly exploited by publishers, because publishers make money from reviewers' free work. But reviewers would do the work for free anyway because that's what they expect others to do.