Or maybe you should spend time on it, by creating a fork with all the good PRs applied?

I would probably do that if the time investment was worth it. For example if it was something I was using on a day to day basis but not for leisurely/exploratory reading.

Even for leisurely reading, you expect an author to still be updating a book several years after it was published? What experience has led you to believe that's a reasonable expectation?

I don’t “expect” the authors to do anything. But I am not going to spend many hours of my time reading a book when I see that the book is not maintained because there are many great books on my backlog that ARE being maintained by the authors/community.

All of my books are in pdf and receive zero maintenance - many of them are still incredibly useful.

I did not make a blank statement about the usefulness of outdated books. But certain topics do get out of date pretty quickly and would be less valuable to a maintained book.

Last commit was 3 months ago, and there are 48 open pull requests ...

Which one of us is accessing the wrong repo?

My mistake. You are right it’s only 50. I still think that 3 months is bit long for not merging any PR for an open source book.

any one else reading this comment should know -- I did look through the PRs and many of them are typo fixes.

Its easy to make demands on open source code maintainers time. Not all PRs and "tickets" need attention. The maintainer does not owe us anything.

I am not making demands nor did I say the maintainers owe me their time. But I do not owe them my time either. And I would rather spend my time on a book that is actively being maintained by the authors or the community.