Because books were so valuable, they were made to last, with quality components and skilled craftsmanship. I once took a course at the local university near me, and got to look at and handle some tomes from the rare book collection. I held a book that was a thousand years old, and I'm sure with proper care it would last another thousand. Books today get battered and thrown out after only a few years at most.
Bookbinding was certainly a skilled craft, with young men apprenticing for many years to become a master bookbinder. They usually worked together with a printers, for both skills were needed to make a book. A couple of years ago I went to a traditional bookbinders in the restored colonial town of Williamsburg in Virginia, USA (an amazing place, lots of traditional crafts and a tonne of great living history, worth a blog post of its own sometime). It inspired me to want to try bookbinding myself.
So how is a book made? Well pages are grouped into signatures, folded using a bone folder and then stitched together on a sewing frame. Endpapers and then glued on and covers are then sewed and glued on to the book, and the book is pressed together in a bookbinding press. It's a little more involved than that, and the book needs to spend a day in the press at a couple of stages of assembly so it is a time consuming process. The covers, often made of leather are then decorated, often either with 'blind tooling' or 'gold tooling'. I am lucky enough to have a father in law who is exceptionally good at woodcraft, and he made all the tools I needed. I have had a go at proper bookbinding with reasonable results, but not yet anything good enough to sell or give to someone as a present.
I've also had a go at a quicker, slightly easier bookbinding method, still hand stitched, but without the need of the sewing frame or the press. It's called coptic stitching, and I'll post a guide to it in the next few days.