Yes, because of course people will do hundreds of hours of work for free.
They will, as it turns out. You'll find countless examples on the internet. Not everyone is as selfish as you.
But many are being subsidized for their work online --- or hope to see a payoff down the road.
Writing a book of any kind is a major accomplishment that relatively few can claim. Anyone who learns that you're a published book author will be impressed. Similarly, if you use your textbook in one of your classes, your stature with your students will rise. You'll also gain name recognition among psychologists because most textbooks are referred to by the author's names rather than the title.
Writing Phase: 2 to 4+ Years. Writing has two meanings. Narrowly, it refers to composing the words in the text, including multiple drafts and several rounds of peer reviews and revisions based on the reviews. Broadly, writing also includes all the necessary reading of sources, compiling references, conceptualizing illustrations, and designing and writing features (e.g., boxed material), learning exercises, review sections, and further resources for students.