system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why do most of the books have between 200-400 pages, and not more or less?
gpt
It is actually a result of marketing and production. Within a genre of books people are generally willing to pay (approximately) the same amount of money no matter the length of a book. People will pay the same for a novel that is 200 pages as they will for a novel that is 400 pages.

If a book is shorter than 200 or so pages it makes the customer feel like they did not get a long enough experience for their purchase. However the longer a book is the more it costs to produce. Paying an editor, layout person, and the physical production of a book all costs more the more pages there are. 

So the combination of costs, what people are willing to spend on books, and a desire to give a good value for the purchase results in a "sweet spot" of 200-400 pages.

Having said all this there certainly are books that are longer and books that are shorter.