As a published author of programming books who has seriously considered (and even talked with a publisher about and tried talking with Epic about) writing a UE4 book, I can speak a little to this.
First, publishers don’t like the bleeding edge, and UE4 right now is the bleeding edge. The publisher I spoke to (who shall remain nameless) was having a hard time accepting that there would be any market for UE4 books. The acquisitions editor I spoke to was responsible for all game-related programming books, and she was setting up a lineup that was 90% Unity books. That’s what has sold in the past, so that’s what they’re publishing in the foreseeable future.
Epic’s move to make UE4 accessible to indies and small shops is disruptive, but publishers don’t see the potential in disruption until somebody has made money on it. A very similar thing happened with my first book. Beginning iPhone Development was one of the first iOS programming books to market, and it was the first one targeted at beginners. At the time, Publishers didn’t like Apple-related programming books because, in the past, they hadn’t sold well. The book came out about during the App Store “Gold Rush”, and it sold like hotcakes, peaking at #23 on Amazon’s overall book ranking. It sold over 100,000 copies in its first year alone. Now, that’s not a lot of copies compared to, say, a well-known fiction author, but in the realm of technical and programming books, it’s a runaway best seller.
Once the BookScan numbers showed the industry that the book was selling really well, every technical publisher started flooding the market with iOS titles and acquisition editors started actively looking for new iOS authors. In the Game dev programming world, right now, it’s Unity. That’s what has sold in the past, so that’s what they are mostly filling their pipeline with.
That’s not the only issue, though. As an author, UE4 is a difficult subject for a few other reasons. The pace of development is insane. We’ve gone from 4.1 to (almost) 4.5 in, what? 6 months? Things are changing fast. If you were writing a book right now, you’d be constantly having to go back and update. That makes undertaking a UE4 book quite a challenge unless you focus the book on a very specific part of the engine (which will have less appeal and sell less). A general UE4 book is going to be partially obsolete by the time it’s finished. Even the three months that it typically takes to get a physical book into the sales channel is potentially an issue here.
Another thing to mention is that UE4 isn’t free and there’s no free trial. I’m not bashing the pricing - I think it’s brilliant and a great value - but that subscription fee is going to be an obstacle for people thinking of buying the book, especially beginner-targeted books. A $30 book that requires an additional $19 a month subscription is really a $49 book in the mind of consumers. Publishers don’t like obstacles to entry, which is why “back in the day”, most programming and technical books came with a CD attached to the back cover containing trial or free versions of all the software used in the book.
Finally, there’s just not an enormous amount of money in writing programming books, and the smaller the niche, the more true that is. Honestly, nobody is likely to get rich writing a UE4 book and most people who are competent to write a UE4 book aren’t likely to have a lot of free time to actually write one.
I think we’ll start seeing UE4 books from major publishers, but my guess is not in any quantity until the middle of next year at the earliest unless Epic takes an active hand in encouraging both publishers and authors.
Fortunately, Epic’s official tutorials and a lot of the unofficial third party ones are excellent, so there’s plenty of material for people who want to learn and I don’t think the lack of books is going to be a huge problem.