It actually stands out to me as odd, given the rest of the article. The same could be said about movies, games, toy cars, etc. Any 1 thing is easy to own a lot of, so long as it's small.
It's when you have multiple collections, or even 1 collection that's too large, that it's a problem.
I have a lot of hobbies that I do only occasionally, and the stuff from them is a little overwhelming. And when combined with all my wife and I have kept because we might need it some day, the hobby room is a disaster area.
We've even gone over our limit on books. To store more books, we'd have to get rid of other things at this point. And most of those books just sit on shelves and never get read. Some might, but overall they're just not actually being read.
To make it worse, books are one of the things that could be digital instead of physical and they could take no space at all. I even prefer reading on my Kindle over a physical book.
In the end, I just can't agree with him on books. (And I don't think Marie Kondo does, either, based on watching a few episodes of the TV show.)
Hm, this is an interesting idea.