Back when books were bought in bookstores, front-matter acted as a book's marketing and sales material, which justified the inclusion of several sections' worth of credibility-building and context-setting.
Today that job is done by the combination of your book's Amazon page (or other store page) and your general online presence as its author.
By the time a reader has bought your book, they've already decided that they believe in it, and you.
Which means that you no longer need to use your precious early pages to set the context, establish your credibility, or try to convince them that your book is worth reading. They're already past that!
Far better to skip all that and just start delivering the meat and potatoes of whatever was promised on the cover.

Michael Bungay Stanier's How to Begin taking this concept to the extreme by putting the book's beginning on its front cover. (The book still contains a short introduction.)
How it helps
The single most important requirement for engaging a new reader is to start delivering on that promise as soon as humanly possible. This is called front-loading the value. That's what advances them from someone who bought your book (but doesn't necessarily read it) to someone who engages with your book.
The hard way to do this is through relentlessly editing every stray word out of existing, raising the value-per-page by reducing the fluff a word at a time. And then sequencing, structuring, and signposting what's coming up so they know it's worth the wait.
And while a fair amount of that may certainly prove necessary, an easy headstart is to just get rid of all the front-matter.
How to make it work
As a rule of thumb, it's surprisingly safe to just start with Chapter 1, deleting everything that comes before that.

Originally written as front-matter, I later deleted everything else and then relocated this short objection-handling intro (400 words) to the beginning of Chapter 1, allowing Write Useful Books to begin without any front-matter at all.
Yes, there are some minor exceptions, like establishing the methodology behind a research-based book, or giving the single most relevant fact about your life. But those exceptions should require paragraphs, not pages.11One bit of front-matter I quite appreciate is from Thinking in Systems by Donella Meadows. There's an introduction of seven-ish pages, which feels justified by the fact that Donella died while writing the book, which her editor wanted to remark upon.
When something feels like it simply can't be deleted, consider relocating it instead:
- Put theoretical context into the Appendix (see: end sooner)
- Put personal details, anecdotes, worldview, and credibility into a breadcrumb author bio
- Unless you're already famous, dead, or revising an already successful book, just delete any preface or foreword
- Reduce important endorsements from a preface to a quote on the cover (or if the details matter, use it later as a story of struggle and success)
- Delete any up-front justifications, disclaimers, caveats, self-deprecation, or other rhetorical contortions, and then sprinkle it back in as appropriate via director's commentary
There might still be something left over.22As mentioned in breadcrumb author bio:
One approach I like is to replace the author bio with a short section called, "Why I'm a relevant source of advice." This allows for the inclusion of your highest-leverage plot points, but feels more relevant and readable by being oriented around the reader's objections instead of your CV. But after deleting and relocating the bulk of it, you're left with either a refreshingly short introduction, or you'll realize that those few paragraphs can be nestled easily enough within the first chapter, feeling as if the train is already on its way.