The printing press is not a single invention. It is the aggregation in one place, of technologies known for centuries before Gutenberg. One thing to remember is that Gutenberg gets credit for an invention that is thought to have been developed simultaneously in Holland and in Prague. The development of mass production paper-making techniques. Paper was brought from China to Italy in the 12th C. but was thought too flimsy for books.
Vellum is extremely durable.
For books that took more than a year to produce, paper was too flimsy. However, for print books, vellum was too costly to produce. The development of oil-based inks. These had been around since the 10th century, but smeared on the vellum used to make books. The religious manuscripts used an egg-based tempura.