The problem with the wood block stamp technology that among others, the Chinese had was that due to the relative weakness of wood you can't print fine details like small letters and you can't print thousands of copies of something because the wood will degrade. What Gutenberg did that was really brilliant was to create a method of not only printing with metal so that small details can be rendered but printing with small interchangeable metal letter pieces so that a printer can rapidly (compared to carving the whole thing) compose a page of writing and then print it as many times as needed. The more copies that were made, the lower the cost was per copy since most of the cost is in making the first copy possible.

Advances in metalworking were necessary to make printing work. It isn't an accident that Johannes Gutenberg was a blacksmith and goldsmith. Here James Burke explains more.