A friend of mine let me borrow Dune 1-3. I loved them and felt I would definitely re-read Dune. When the deluxe box set of 1-3 came out I bought it but it is just sitting on my shelf. I do plan on rereading them but probably not for awhile. Sometimes I also just like having the books I’ve read on my shelf as “trophies”.
“Trophy” book collecting is definitely something I can get behind. My personal library is 80% books I plan to read and 20% books I’ve read but which I want to keep (i.e. trophies).
Some of these books are just relatively rare. Not expensive or anything, but just harder to find. So I keep them, even if I’ve read them. Others are books that I quite enjoyed and that I do want to read again someday, so I keep them as an insurance towards that: that way, if I want to read it again, I won’t have to go through the trouble of tracking it down or buying again.