Most published books either have a track record as self-published break outs, and/or they're trend chasers, and/or - as the article noted, but didn't say enough about - they have authors who fit a known demographic with known tastes and can be marketed on the strength of the author's story.
The real reason so many books are published is because it's a volume game. Most books are actually profitable - barely - so they need to keep churning them out to make adequate aggregate profits.
It's true that most of the money is made by a few tens of authors, but that doesn't mean no money is coming from the rest.
The tiny number of high prestige titles are cultural loss leaders which give publishers a cover story that they're really about Serious Literature and aren't just content mills.
This used to be a credible excuse when Serious Authors were still a thing, but it's looking more and more threadbare these days.
Serious Authors used to be household names, but hardly anyone can name a Recent Serious Author now. Critics still criticise, competitions still award prizes, and review editors still review, but most of the money and most of the interest is elsewhere.