I guess one needs to consider the US is geographically much larger and most land doesn't actually contain people. Considering the density is wiser, but even still. Libraries per occupied area still isn't a good metric. There is no good metric.

What's more important is the qualitative offerings and impact:

1. Spectrum of a. most common services and collections offered everywhere to b. the most comprehensive of those offered by a specific library.

2. What people can do at them: read, research subjects, borrow things, accomplish tasks, host meetings, etc.

This is very hard to measure and not something a business person running the government "like a business" would understand.