Why are there often blank pages at the end of books?

I suppose its for people who make notes on the books. When I first finish a book I use the pages to write bits of information in the book I want to read up on.

Not much today. But once, they were the result of cutting and folding to create certain page sizes, were used to help "stiffen" a book and to add pages for notes and comments -- and some additional printing, if needed.

This has largely become a tradition. Here are two discussions:

[ teched.vt.edu/gcc/HTML/PrintingsPast/EvolutionOfBook.html ]
[ imprint.uwaterloo.ca/story.php?f=2&t=6725&i=&v=f&story=6725 ]
[ links no longer exist ]

In printing, the pages of a book are actually printed on a huge sheet of paper and then folded up prior to being cut... In some older books, you'll find some pages that have not been cut, and so you have to tear them to read what's inside...

The group of pages (usually 16 pages) is called a signature. If you look straight down onto the top of a hardcover book, you'll see groups of pages... a book is made up of several signatures.

Sometimes the author hasn't written enough to fill all the pages of a signature, and this may result in some blank pages at the end of the book.

https://en.wikipedia.org/wiki/Intentionally_blank_page

If a book with 318 pages of content is printed using 32-page signatures, it will require 10 signatures, 320 pages in total. At the very end of the book — that is, at the end of the last signature — there will be 2 unused (blank) pages.

If a printer's document processor has been designed to skip completely blank pages, notices may also be required on intentionally blank pages to prevent incorrect page numbering.

Also, a blank page at the beginning or end of a book is called a flyleaf.

http://www.yourdictionary.com/flyleaf