I feel like the article glosses over a key point: Even on the high end, there were only 11 books that sold more than 500,000 copies. If I can spend two to three years writing a novel and my best case scenario is having it sell a couple hundred copies Isn't the best case scenario here that you are the top -selling author, selling over a million copies? I feel like the author of this post is just assuming that they are…
As the article states, just 0.01 percent of books sell more than 100k copies, it's not enough to be a great author (not average, but better than 99% of them) you'd need to be somewhat exceptional (better than 99.99%) in order to earn a salary from books.
IMHO there's just too much competition, there so many more "top 1%+" authors in any genre than anyone can read, and given the economics described in this article, many of them don't even bother with publishing and offer their amazing writing for free.