Bingo. If no one is buying a series that sends out the wrong impression, not just to the writer, but to their publisher.

Both self-published and publisher-supported writers need sales figures. They’re a barometer of public interest.

If the books aren’t selling then it suggests they’re not popular, which can make a publisher think the writer themselves is bad, or that the story simply isn’t a draw for people, resulting in the withdraw of support.

For a self-published writer it’s often even worse. If the books aren’t selling then it suggests either the story isn’t grabbing people’s attention, or the market for that type of story has declined to the point that it’s no longer worth publishing. In that case the writer may give up on writing, or give up on publishing their story and never bother to share the rest of it with the world.

To get more personal for a moment, I’m a writer myself. I’ve self-published in the past. This isn’t my day job, it doesn’t pay the bills, it is a little side money from doing what I love. Even with it just being something I do for the love of it, actually putting together an ebook to publish is a lot of work. If a book doesn’t sell? I’m not going to go to the effort of making the sequel into an ebook. I need to know there’s readers interested in it if I’m going to go to all the trouble of getting it self-publish ready.