It probably has a lot to do with taste. My kids have tons of books because it's what I like so it's what they know. I like shopping for clothes, but I prefer shopping for books. We have so many books. I teach my kids to take care of their stuff, but nobody's perfect. We have so many books that I don't really care when I have to throw out a book because the cover got ripped. It hasn't happened often, but they're 2 & 5. The other day the five year old threw every book on one shelf carelessly on the floor looking for one book. I made him clean it up. It did cross my mind that if we only had library books my kids would not be this comfortable with books. I buy most of my childrens books used and in good condition for less than a dollar. But if your kid loses or breaks a book you borrowed, you're paying full price. (I lost a cd I borrowed from the library-$35.00).
People keep saying everybody has access to a free public library. It would be an extrordinary kid who has the EF skills to do all that and never lose the books. The librarian will give you some slack, but my friend's kid can not use her library card because she has five books somewhere around the house she can't find. Everybody knows a story about some unlikely kid who did use the library successfully, but still. My kids library books stay on a top shelf and I told them not to use a stool to get them, only ask me.

Youth lives by personality, age lives by calculation. -- Aristotle on a calendar