Readers will generally only rate and review a book once they've finished it.
But "finishing" doesn't require that they've read 100% of the pages — only that they feel as though they've reached the end by virtue of having reached a satisfying conclusion.
Simple solution: put the ending sooner, recategorizing the remaining chapters as part of the Appendix.

The Workshop Survival Guide (by Devin Hunt and myself), showing how we put the ending sooner by moving four advanced chapters into the Appendix.
How it helps
It's always hard to decide what to do with chapters that are valuable-but-situational (such as niche, nuanced, and expert topics). Not every reader needs them, but the ones who do will tend to receive a ton of value.
As such, these chapters are hard to cut, but can end up feeling like a slog through the book's final stretch, risking abandonment right before the finish line.
"When you do comedy, you have to start strong, and you have to finish strong.
Those are the tricks, right? You can’t be like pancakes, all exciting at
first, but then by the end you’re sick of them."
— Mitch Hedberg
By "concluding" sooner, you ensure that a higher percentage of readers will reach the "end" (and thus rate and review). And you do so without losing out on anything, since the most engaged readers will simply continue reading into the relevant bits of the Appendix.
Some topics require more of these situational chapters than others (which, at an extreme, might require fully nonlinear navigation). But when you're only dealing with a small handful of situational chapters, try putting the ending sooner.11To attempt to put a number on it, you could consider moving up to a maximum of 40% of a book's chapters into the Appendix without it feeling overly bizarre (assuming there's still enough core content remaining to feel complete and canonical).
It's one of the simplest interventions you can make, and it works surprisingly well.
How to make it work
Given that many books' Appendixes are essentially empty calories, make sure you've let readers know about all the great stuff you've put in there.
Potentially using something like inline indexing, director's commentary, margin notes, or a map of progress that includes the Appendix.
Additionally, introduce your Appendix with a bang, providing a high-value opening and promise of what's to come (similar to what is done in standalone parts). In particular, put these situational chapters at the start of your Appendix, delaying any other backmatter for later.
In general, if you're putting the ending sooner, you'll want to treat your Appendix not as just an afterthought, but with all the care and craft as any other core part of the your book.
Takeaways
- Move valuable-but-situational chapters into the Appendix, allowing you to put the ending sooner
- Signpost the existence of these chapters throughout the book's content and navigational aids
- Invest in a strong start to your Appendix, complete with front-loaded value and reliable navigation