And you're going to be doing most of the marketing yourself in any case.
For most people, writing a book is an investment whether you go through a publisher or not. Unless it's just a passion project, you're presumably doing it for your career/brand/etc., not to make a meaningful amount of money. If you are evaluating how to go about a book project based on pure financial ROI, the short answer is you should probably do something else.
- As someone else noted, you can put free eBooks online. If you're writing a book for visibility, being able to distribute free copies (or customized versions of free copies) might be a benefit.
- You don't need to conform to publishing industry length standards. If 75 pages cover the topic, you get most of the benefit of publishing "a regular book" for a lot less effort.
- You're on no one's deadline but your own. This has pros and cons but does let you better work a book around life, work, and other projects.
- The style, format, etc. is all up to you. Again, pros and cons.
I have made (a bit) more money with publishers than self-publishing. I'm also not sure if I'd go with a publisher again barring a strong reason to do so.
Sure, but you could hire independent specialists with exactly the skills you need rather than relying on your publisher's choices, and still retain overall control of your work and the process of distributing it yourself.
If a publisher provides some degree of overall project management as well then evidently there is also a space for professionals to offer that service independently to those authors who don't wish to get involved in such matters themselves.
Even if you have the patience to do this part, most probably the book design will look amateurish.
Perhaps, but the bookshelf next to me clearly demonstrates that big name publishers are capable of producing poorly designed, crudely illustrated, naively typeset, negligibly edited rubbish too.