>> Maybe publishers should JUST pay authors WELL, and get a book every 2-3 years

There are a couple problems with this approach.

Firstly, while the median income is 20k, the book business is like films or music; ie not evenly distributed. At the top end are a small number of successful authors. They effectively subsidize the publishing house while the house throws advances at authors hoping for the next big whale.

Many books never earn back their advance. Meaning if the author was paid out of royalties they'd make less, not more.

Making advances bigger would result in fewer advances. The pot of money is finite.

This is all happening in a market where supply is unconstrained (everyone thinks they can write), and demand is very limited.

And before we discuss the value, or lack thereof of having an intermediary at all, it should be noted from your link that the median for published authors is higher than self-published authors. So clearly they seem to be making authors more valuable.

In truth of course, most (published) books aren't terribly valuable. Like music and movies most float to the bottom.

So no, the answer is not "pay authors more".