I think smaller apartments and lack of storage space might be a driver for buying less books. However, while I do feel modern apartments are smaller, I don't know if this feeling is true.
"In general, small rentals are getting smaller and large apartments are gaining square feet. More precisely, two- and three-bedroom apartments have been adding more floor space in the last decade, while studios and one-bedroom apartments (the dominating floorplan among new apartments) have been getting more and more compact."
