The contributors are mostly writers of one flavor or another. They are qualified because they did the hard work of creating their pieces. Everyone is qualified to talk about class, and if we enjoy writing or want to write, to write about class. And their qualifications would have to include perseverance. That's sort of unusual for a book like this.
Class systems are about rules of order and hierarchies.
I'm simplifying it in the extreme when I say there is a class system around writing genres. Usually writing considered appropriate for political analysis is filled with facts and strong sentences. I like that kind of writing. It gets my blood up and gives me tools to work with. It makes me feel a particular kind of righteous.