I would bet this is one of those more subtle long-term effects that nobody really saw coming... when Google refocused search with an eye towards commercial results, I imagine it deprioritized a lot of the older, more innocent informational content lying around
Google seems to have decided that Wikipedia is the only blessed noncommercial source of intelligence.
I guess, if I were to put it strongly, I'd say: using Google is not like using the Internet any longer.
FWIW, HNers may wish to check out Yewno[1], a knowledge search engine based in Redwood City that I've had the pleasure of being (tangentially) involved in.
[1] http://yewno.com
[2] Yes, I know this is indexed. It just frequently gets buried in my searches.