Rob, if, as you said, "art is simple", galleries would include a mix of subject matter, from portraits to landscapes to abstracts to street. However, that is not the case. Galleries are chalk full of anonymous, in-your-face, all-too-tight, bleached-eye portraits, Holga fuzz, and out of focus composites, but are almost completely devoid of landscapes or nature. Why is that? It is because photographic art has become an academic popularity contest with prizes and accolades for those who are content to re-create what has already been successful. I mean really, if I see one more Diane Arbus rip-off of a stoic set of twins, or a 20-minute exposure of an ocean shoreline, I'm going to rip it off the wall and urinate all over the thing. At least THEN it'll be unique.
Many photographers, especially those in BFA or MFA programs, are programmed to photograph only what is expected, in a manner which is expected. Personal vision is valid only if it conforms to a narrowly defined criteria of contemporary "standards". Such myoptic criteria for "art", enforced by academics, publishers, curators and gallery owners, dumbs down photography. Reduces it to banal, meaningless images created for the sole, irrelevant purpose of gaining peer acceptance.
I cannot speak for Brooks but am assuming that some of this is what he is referring to, and I think he's correct. To be honest, I wish he had gone a bit further, been a bit more critical. Photography (any art, for that matter) needs to be meaningful for both the creator and the viewer, and it much of what I see today, I simple don't see much of that. Instead, I see of lot of photographers trying to impress other photographers.