I'm not sure about the data; Buenos Aires reported 25 libraries in a year and now it disappears from the ranking. I don't think they closed down their libraries in a couple of years?
I'm pretty sure we haven't lost that many libraries, and I have even seen new ones in recent years.
It also doesn't do much to account for differences between libraries. A small, poorly funded library is probably going to be less interesting than a large, well funded library.