Regarding academic books, they come out in very small editions, because there aren't that many buyers. This makes them necessarily more expensive than books for the common markets. Besides, because they're written for the needs of experts or students in the discipline, they're not necessarily easy to understand without knowledge in the field.
Well, partly that depends on the field. I alw<ays wanted to dig deeper into some areas of Archaeology, but I never found books at an affordable price. Or with other parts of science.
Of course I could go into the university's library, and read books there.
I think that I'm a niche no-one thinks about : The enthuisiast, who has had a little bit of expert knowledge, but wants to expand that. Through reading books.
But I can't expand it that easily, because of my working time I can't go into a library at any time, and at the same time I can't afford buying certain books.
For example, the newest translation of the Beowulf only lists English-language books. Even although the translator appears to be German.
He doesn't even list the German translation of the Essay of Tolkien on Beowulf, although it exists ( I have read it ). So, if I want to expand my knowledge on the Bowulf, I have to read it in English, because there is no German-language book available. And that even although a partial translation into the German language is cited in the annotations of that new translation.
And that's just an example.
Even although the sitiation has gradually improved within the recent decades, writing "popular science books" still seems to be frowned upon in the German academic areas. I often wrote rants about that already. But there still is enough NOT to get.
For example, I don't even know a German-language book on how the Bible actually evolved. The Septuaginta translated into German language is not cheap.
And I believe that this is also the reason why projects like "OpenScience" have evolved in the first place . Because science book editors are sitting on their monopoly status and most certainly don't want to make lesser prices. everyone who wants a ceretain book HAS to pay those prices - because of "knowledge monopoly" ! To me, that's some kind of blackmail : "If you want that book, well, then youi'll have to pay OUR prices." I assume that OpenScience has evolved to battle that.
https://en.wikipedia.org/wiki/Open_science
Quoted from there :
Proponents of open science identify a number of barriers that impede or dissuade the broad dissemination of scientific data.[14] These include financial paywalls of for-profit research publishers, restrictions on usage applied by publishers of data, poor formatting of data or use of proprietary software that makes it difficult to re-purpose, and cultural reluctance to publish data for fears of losing control of how the information is used.[14][15]