The reason is: paper. Dead tree books weigh a lot and waste space. Therefore owning a library is a cost. Costs to move, costs storage space, costs effort to collate and maintain and protect.
E-books do not have that cost. Having a hundred e-books in your purse is a normal thing. Having a thousand? Well, it might make sorting through your personal equivalent of a branch library a little more fussy, but it won't weigh more or waste space.
People may not have more time, but they can divert time to books, and they can divert re-reading time to new-book reading time.