> In a traditional publishing context failure is an option. Many books don’t get published. If the pitch is not good enough, it gets dropped. If the first few chapters is not good enough it gets dropped. If they can’t polish it to satisfaction with an editor the work gets dropped. I’m not saying that quality is the only rubric the publishers use to judge when to drop a book vs when to publish, but it is heavily judged at every step of the way at multiple gates.
Maybe I come from a different writing "culture", but most of the books I see being self-published are restructurings of works previously published online in serial format (if nonfiction, as blog posts; if fiction, as several-times-weekly mini-chapter serial fiction), where the popularity of the output is effectively pre-determined, as the creation and publication of a standalone purchasable book is entirely being driven by demand for such by the existing audience of the source material.
Further, those serial publications are often, these days, being sponsored via Patreon, or published via apps that charge to unlock chapters and give some of that money to the author, and so forth — so the author already has an income stream from their work, that they can reinvest into their work (through editing) to multiply the amount they're making from their work.
In that sense, "editing" for their books becomes exactly the same as "editing" for e.g. a YouTube channel: something where there's a direct proven correlation between "production values" and "attach rate", where that and a steady existing revenue stream will be enough to get you a business loan from any sensible bank.