As an artist who very much enjoys this style I agree wholeheartedly with your premise but not your conclusion. ISTM that that this is precisely what the article is about, albeit presented in a breezy did-you-know-this-fun-fact way rather than the more plodding style of academic writing.

I thought it was an excellent article and I'm baffled by your suggestion that the author was oblivious to or indifferent to the symbolic language in the paintings, even if he didn't explore each individual one to the depth that you might have preferred.