The author of this article makes the point that Substack pays ~90% in revenue, versus traditional publishers which do ~10%.
While this is true, I do think the author seems to deliberately avoid mentioning the self-publishing platforms like Gumroad, Podia etc which allow authors to keep 95-96.5% of revenue when publishing books, and also have a direct connection with people who bug the books through emails. I say this as someone who published through one of these platforms. (Also, there are other newsletter providers which charge even less of a commission, like Revue charging 5% or Ghost or ConvertKit charging a monthly fee based on the number of subscribers, which could come out to below 5%)
A real (financial) pull of publishing a book via a monthly, paid newsletter is the higher revenue per customer. A customer won’t pay more than, say, $40 for a book. But they’ll more likely pay ~$120 by paying $10/month for a year. See also how Steven Sinofsky is publishing his book series Hardcore Software on Substack with the option to pay up to $300/year to get a final, printable PDF edition of the series once finished. I paid $100 to read this series for a year and one of my friends went for the $300 option.
Holding on to publishing rights is a huge difference when going self-publishing or newsletter-first. When I worked with a traditional publisher, only then did I realize I have no rights to publish my words without publisher consent: this was when I asked if I can share drafts of my writing in public, and the publisher said this is down to approvals on their end. This realisation was a reason I ended up self-publishing instead. As the author of the article notes, by keeping publishing rights, it’s always an option to sign a contract with a publisher for a print book.
What is not written in the article is how self-publishing makes a lot more (financial) sense once:
1. You have enough of a reach to not benefit much from the - sometimes surprisingly little - marketing that a traditional publisher does
2. The association with a publisher brand is no longer a priority.
3. You don’t need a publisher helping you finish a book pushing you with deadlines (they sure help!)
4. You are ok paying for - or doing yourself - editorial things (development editing, copyediting, proofreading)