It has to do with priorities: who gets what and how much.
Self-published bestseller Hugh Howie spells it out from one to ten in this article — including some history — and rates the importance of the different “stakeholders” thus:
1: Readers
2: Writers
3: Editors
4: Bookstores (digital only)
5: Libraries
6: Books (as in paper books)
7: Narrators
8: Cover artists
9: Publishers
10: Critics
The priorities part comes in when you swap “author” for “publisher.” A partial list might look something like this:
Bookstores (physical)
Libraries
Books (as in paper books)
Critics
Cover artists
Editors
Narrators
Authors
Readers