Because the same people who buy expensive Starbucks coffee drinks need a place to hangout and read books and feel even more snooty. Wear a turtleneck sweater, and suede shoes. Wanting to secretly, hoping to, bump into a woman wearing a long skirt and flat shoes and have some kind of intellectual romantic comedy on the book topics you like to read. -- and mutual hate of Trump.
I just went to one on Saturday. It was pretty busy, but obviously not busy enough, after looking at their stock price. There was a Borders store a couple blocks away which I loved going to. But it closed many years ago. Sign of the times. (BTW, I don't wear turtlenecks or suede shoes. More of a jeans, tennis shoes and t-shirt kind of guy. I just like book stores.)
For the same reason newspapers exist. At one point they become value stocks and some large investor like Warren Buffett buys a stake or they become takeover target for likes of AMZN.