In English, stockpiling books without ever reading them might be called being a literary pack rat. People in Japan have a much nicer term for the habit: tsundoku.
According to the BBC, the term tsundoku derives from the words tsumu ("to pile up") and doku ("to read"), and it has been around for more than a century. One of its earliest known print appearances dates back to 1879, when a Japanese satirical text playfully referred to a professor with a large collection of unread books as tsundoku sensei.
While accusing someone of caring more about owning books than reading them may sound insulting, in Japan, the word tsundoku doesn't carry any negative connotations. Tsundoku isn't the same as hoarding books obsessively. People who engage in tsundoku at least intend to read the books they buy, in contrast to people with bibliomania, who collect books just for the sake of having them.
There are many reasons someone might feel compelled to purchase a physical book. Though e-books are convenient, many people still prefer hard copies. Physical books can be easier on the eyes and less distracting than e-readers, and people who read from ink-and-paper texts have an easier time remembering a story's timeline than people who read digital books. Of course, the only way to enjoy those benefits is by pulling a book off your shelf and actually reading it—something people practicing tsundoku never get around to.