My daughter does this, has done since she was a little girl. Once, I asked her why - she just shrugged and said she preferred it that way, no specific reason.
Fair enough, I thought. Her books, her shelves, no one was getting harmed by it - and I moved on.
Why is everyone getting so butt hurt in this thread about it?
I keep the books I read for sentimental reasons and because usually they have notes in them. But I definitely do not look into them on a regular basis. Even the books that I do reread or look something up in I do this maybe 2-3 times a year. Those are the frequent use books. Most I “use” less often. Now, if I open a book once a year or less I can also put it away in a box, the basement, or hide it somewhere in the closet. It does not need to be easily accessible. I also have raclette that I use once a year and it is also crammed in the back of a closet because I need other things to be quickly and easily accessible. If anything, it is me who uses the books as decoration as I keep them on display in a bookshelf - not because it shows my intent or interest to reread them. This is to say that while it looks impractical in the first glance, it doesn’t mean the books are less used or used more often. The way they are stored doesn’t need to mean anything. You can also find some joy in finding the right book by just remembering its thickness or size or color or where it is stored because you actually do pull it out so often. I even remember having this kind of “ha, gotcha, you thought I wouldn’t find you immediately, huh, you’re so wrong kiddo” feeling when I pulled out a favorite book from a bookpile when I couldn’t see the covers.