It doesn’t even have every book published in the UK, because there are a lot of books, especially at the beginning of the printing press period, which does not exist in any known copies anymore.

Not to mention that the policy of collecting ephemera is a relatively new one, so most older ephemera doesn’t exist in its collections either.

Borges’ Library of Babel was the size of a planet and had not just every book in every language, but they were interspersed with books full of gibberish and people spend their lives in the library looking for the book that will give them all knowledge but never find it.