There is a lot of diversity in journals, but MDPI has a very atypical model. More famous/prestigious journals, as well as more niche society journals are able t

There is a lot of diversity in journals, but MDPI has a very atypical model. More famous/prestigious journals, as well as more niche society journals are able to get PIs to work as editors for free just for the prestige of being affiliated with them. MDPI seems to have a very hard time finding volunteer editors and reviewers, to the point that they are aggressive and annoying- I was getting so many review requests from them (many per week) that I blocked e-mails from their domain, when polite requests to stop were ignored. That said, I did publish a paper with them once, and it was a positive experience.