This word is relatively new, used in 1993 and is a term journalists use to talk about the reporters who comment on the news. Mostly commentariat is used in reference to commentators on American political affairs. The word is a blend of commentator with the suffix -ariat.
My basic hypothesis is this: the people who run the media are Humanities graduates with little understanding of science, who wear their ignorance as a badge of honor. Secretly, deep down, perhaps they resent the fact that they have denied themselves access to the most significant developments in the history of Western thought from the past two hundred years. There is an attack implicit in all media coverage of science – in their choice of stories, and the way they cover them. The media create a parody of science. On this template, science is portrayed as groundless, incomprehensible didactic truth statements from scientists – who, themselves, are socially- powerful, arbitrary un-elected authority figures. They are detached from reality. They do work that is either wacky, or dangerous, but either way, everything in science is tenuous, contradictory, probably going to change soon and – most ridiculously – hard to understand. Having created this parody, the Commentariat then attack it, as if they were genuinely critiquing what science is all about.”
― Ben Goldacre, Bad Science
“Unfortunately the epistemological standards of common sense—we should credit the people and ideas that make correct predictions, and discount the ones that don’t—are rarely applied to the intelligentsia and commentariat, who dispense opinions free of accountability.”