I also agree with the "people love the idea of bookstores" analysis. And also: since the book of ecommerce, megastores are the less convenient option to
online megastores, where you can get services like recensions, "if-you-liked-that-you'd-like-this" recommendations, and, often, free expedited shipping,
plus the variety that a bookshop and, above all, a generalist megastore won't carry these days because it doesn't sell this easily.
I remember when going every Saturday into bookshopping was interesting- stopped doing that about seven years ago, when in my city most great bookshop were refurbished or went into a crisis (changing owner quite fast) or closed down. Now we got a couple of specialised stores (Cortina right straight before the university and Hoepli- with a lot of specialities, even if it's not as good as before) and the ever-present Empire of Feltrinelli (hint: in a country where the book market is small, they have bookshops in cinemas and train stations
). Of these, the former are still marginally enjoyable, the latter are too standardised. Which makes bookshopping for presents not the best thing ever.
And, as
eric11210 pointed out, there's the question of English or foreign language books. Nowadays it costs a lot less buying them online (even with shipping fees) than buying them into physical shops, because there are duties (what was called once upon a time
book's franc/pound); plus we're more informed into what's published now abroad. So all the thrilling of the American Bookstore or the English Bookshop or the Libreria Francese Ile-de-France can't exist anymore, if not for some pretty volume or the general old-books sale.