Several reason, you enjoy books, both the tactile sensation, and the smell, the fact that you also enjoy reading them, and that in your mind older books, or used books gains more value in being used, in being well red, in being loved.
So when you put this into a single location, that is usually cramped, stacked up to the ceiling, so much so, that there might be some bookpillars that are roofbearing, they got the charm of being cramped and small, and the smell of lignin and dust just adds to it, its silent, few people, and a bit outta the way, allowing you time to check the books for something interesting, and here you judge the book by its cover. Maybe something that fits your taste, or at least the spine of the book, maybe you see some keywords that increases your appetite for reading, maybe the lastname of an author you enjoy, maybe a spine that shows its age, as being in bad conditions, and you want to give it a home. It takes your out of the modern era, takes you to the 90s and beyond, no harsh lighting, just old warm light that is just cozy, and not harsh on the eyes, lets you skim the text on the various spines. The sense of nostalgia seems to slow down time, there is nothing but you and these books. The owner is someone up in the age, grey hair, smile lines, and reading glasses, and they are enjoying a book as well, you made eye contacts on entering the store, and the ringing of a brass bell above the door sent you straight into the world of used bookstores.