He's in the social sciences. It makes sense he'd focus on that. It is possible to publish nonsense papers in STEM journals too, hence the stories about "tortured phrases" that cropped up a few weeks ago. However there's no particular reason a philosophy professor would be aware of those journals or have any motivation to explore their integrity; naturally he will focus on journals about subjects he understands better than e.g. electronics or medicine.
I hope that's not his reasoning, because it is rather lazy. In order to know whether or not a phenomenon is a problem that matters you need to get an understanding of what is "normal" or not. Fraud is common in all fields in life. Someone who obsesses over the fraud present in one ideological wing of their field and nothing else would not be someone that I take seriously, personally.
