Some years ago I did some volunteer work where I had to go through some thousands of old books at a library and find the valuable ones. I came to the conclusion that around 1850 there was a "phase change" in printing. You could tell the books before 1850, they were works of love. After 1850, I think mass printing took off, or something, but you can feel books were not luxury items anymore.
In any case, this gentleman here has in his possession a book before 1600, and he writes on its margins. Maybe this was a form of conspicuous consumption. But just look how gorgeous that book was. And the guy just scribbled some stuff on it.