Good observation. This makes me think of all the useful content Wikipedia doesn’t link to though.
Really, I am of the perspective that a machine-grokked indexing system will always be less useful in a significant set of edge-cases than a human-curated index due to such factors as language ambiguity and gaming of such algorithms. As well, the sheer size of the internet requires ranking the pages to ensure the most useful links are properly denoted as such.
WP, being likely the most important and useful crowd-sourced and -built human information system, it is up to us to both keep it funded and add the information we deem important.