I don't understand why he holds on to books? I have a couple of books that I hold on for frequent references, but the rest I just donate when I'm done. I'm sure

I don't understand why he holds on to books? I have a couple of books that I hold on for frequent references, but the rest I just donate when I'm done. I'm sure my house makes it look like I don't care about books, but I would rather my shelves are a TODO list of things to read, not a dust gathering collection of things I've read in the past.