The argument from authority (e.g., publishing mafias) fallacy is ripe in academia.
Same situation with textbooks. Besides profit and trying to become famous, there's no reason why a professor should publish through a traditional imprint or publisher (Pearson, Cengage, McGraw Hill, Wiley, Taylor and Francis, Elsevier, etc.). LaTeX, a Creative Commons license, and a homepage at the university department (and perhaps a GitHub/GitLab repo) is all a professor needs to make textbooks available worldwide.
Writing and editing a textbook is indeed a hard task. Yet, having the end result behind paywalls and arbitrary pricing isn't worth it.