How a book (or newspaper, or magazine) is made is:
- A giant roll of paper (like you see in a receipt printer) gets printed on both sides
- The giant roll is cut into giant sheets
- The giant sheets are folded over into a stack of, like, 8 or 16 "pages" thick (you fold it in "half" 3 or 4 times)
- These folded-over things are attached to each other (with thread, glue, staples etc)
- This big thick thing has the edges cut
- Whatever the hell for the cover/outer binding happens. So this is the "end papers" (the colored paper connected to the hard part of the hard cover), the cover, maybe a little ribbon to keep your place, and/or the dust jacket
Please pay attention to steps 3 and 5. Now...how would you make a book with 15 pages? or 9? Or 33? Keep in mind that ALL* books are made, at-scale, in factories, on presses and equipment that are standard sizes. Making a book that is longer is easy, just have more stacks of things. Having a book that is shorter than 8 or 16 pages is tricky, cause, like, how do you do that.... You CAN do it but it's a giant pain in the ass. And no factory is going to do that unless they have a really, really good reason to do it. Asking nicely is not a good enough reason.
So the page numbers you're referring to is probably everything in-between the cover/end papers. So the title page, the "this is the legalese" page, and the story itself. Open up some kids picture books and count ALL the pages between the end papers and you'll find it's one of these nice even numbers divisible by 8 or something. You can do it with larger books/magazines/newspapers, too, but those tend to be way more pages and that would suck more to do lol
*"But Chase!" you say, "what about print-on-demand books? Those aren't made at scale!" Well, if we want to be extremely literal, yes! That is true! Because they are not making printing plates for your one book, because that shit is so expensive. HOWEVER, they are STILL using presses and equipment that are fixed sizes. They have a process set up to make these things as fast as possible, so there might be multiple books being processed at once. But the folded-over thing (I feel really dumb forgetting what it's called you can tell all of my press knowledge is from working the presses and not actually learning how to manage them)