Early books were bound in the codex style with the cords, and sewing of the hinges, securely glued to a flexible covering of leather. The cords were worked around the back into stout wooden boards, to protect the inner pages. All this, collating, sewing, gluing, leather working, had to be done by skilful hands.
As printing became easier there was a need for speeding-up the binding process. Nowadays the pages can be printed, folded, collated, sewn, and glued into bookblocks, all by one, or more,machines.
Similarly boards and covering materials are made, carefully to measure, and assembled. These are then fairly securely encased around the book block. I say "fairly securely" because that is usually the weakest point in the construction. It does not take much wear and tear for a poorly case-bound book to have loose covers.
Modern case-bound books still have the cachet of being "hardback", although the practicality of tight-bound limp bindings is gaining popularity and helping (rightly, in my opinion) to bring the paper-back out of scorn and disfavour.
The popularity of case-binding is due, in the main, to the ease with which so much can be mechanized. For example a 200 page diary can be printed, bound, and shipped half way round the World, from China, and retailed for less than £1. (The 2020 price at "multi-bargain" types of shop. It has been stable at that for several years.)
Case binding can readily be undertken, with excellent results, by any competent craftsperson. The book block can be machine ~ or hand ~ sewn. The covers can use a variety of materials ~ leather ~ hessian ~ cotton cloth ~ book cloth. Machine-made books invariably use cases covered in book-cloth, which can be easily worked and also readily takes die-stamping for titles or decoration.