The first one was an accident of sorts. I went to a lot of conferences in the late 90's, early 2000's around the world to hawk our wares, and wanted a way to supplement the returns, so I'd visit user groups and do some training with them.
I started with simple notes, which gradually grew up to about 120 pages, which accompanied a full day course. After one event in 2002 I was pestered to sell extra copies of the notes, by folk who weren't there.
Initially I resisted, they weren't written with that in mind, but capitulated, edited, added a bunch of things, and sold them for $50 plus postage - I cleared about $25 per copy and sold in total about 1000 copies.
The second one was more deliberate, although again borne out of a 2 day training class. That costs $200,is PDF only, and I've sold maybe 300 or so. I update that one and am currently working on the 4th edition. (in 13 years)
It's not terribly profitable. The time it takes to write is insane. Unlike casual speaking or blogging every tiny detail has to be checked. It has to have a coherent voice. It ultimately needs to teach difficult concepts and make them easy.
To describe the topic as niche is an understatement. It's a pimple on niche. If it was 100 times bigger it'd still be a small niche. So upside, no competition. Downside, tiny market. Its not really profitable, but it is a nice side project.
So maybe the right answer to your question, for most people, is that they haven't accidentally tripped into it (yet).
However, looking at it ex negativo, I can tell what convinced me to write this particular book: A subject to write and learn more about and two co-authors to write the book together with.
Making writing a collaborative effort is enormously helpful, not only since it helps with staying motivated but also because it allows you to more easily break down what can otherwise seem like a daunting amount of work. We even organically arrived at a "pull request"-style review process that allowed us to release quickly and iteratively without getting a third-party editor involved, which could've been a bottleneck and hence might've slowed down progress (more on our writing process: https://progmot.com/post/self-publishing-a-book-with-almost-...).
Another key factor was a relevant target audience we could relate to. Knowing that there's a problem (How to become productive with developing Spring-based applications on AWS?) which hadn't been explored and addressed in an in-depth, comprehensive manner before and being aware that we weren't the only ones having that problem but a significant number of people from our peer group were facing the same issue, was vital for our decision to write this ebook.
No, we really all are not, and not everyone does. I don't write because I have nothing to say that hasn't been said more eloquently. It's also a hell of a lot of work and unlikely to break even in strictly financial investment, valuing my time at $0.
As for a fiction novel, I don't have any storyline in mind. I have images in my mind, short videos/films I find enjoyable, but not a grand story that could fill 400 pages.
I'm also not a famous person, so my autobiography wouldn't be of much interest.
- how much you gain writing a book about a technical viewpoint you have (from researching all of your "instincts" and figuring out a way to explain them to beginners)
- you don't have to start with a book - just write blog articles about sub-problems in the space
- a book can literally just be a collection of blog articles (see Freakonomics: https://freakonomics.com/blog/)
- it's not about the money - unless you've spent the last decade being well known in your field, most folks will likely not hear about your book. Doesn't mean it isn't a worthwhile endeavour.
(I write this having written https://useeffectbyexample.com/ for my React blog's audience, has made low 4 figures)
An idea for a book did occur to me a couple years ago: I thought I might write down everything I know about throwing renegade-style rave parties. What kept me? I'm not certain my knowledge is unique enough to be useful, and I think maybe it's better for people to figure it out organically, as part of a community. I wouldn't want to help people throw such events as a business.
Also I have many things that I could write about and do not know what are all of the things that I will want to write about.