It comes down to the curation. Those books were the result of one or a few people consciously deciding what was important to include. They made value-based decisions to decide what would make the cut. Constraint forces choices which lead to a more valuable experience.

In addition to the physicality of the book, browsing them meant the viewer didn't need to sort through the cruft (someone had already done that work for them), allowing them to use their own energy/thoughts to build upon that work resulting in new ideas and creativity.