1. If we have time to enter something into a knowledge base of any kind - then we have time to just jot it on a piece of paper.
2. If we dont have time (or think it is important at that moment) then what solves the problem for us is not a knowledge base, but search.
You see the thing about Google and Facebook etc, is that if they were collecting all this information about me, and it was treated like medical information about me it would be far more useful to me (and far less useful to Advertisers).
I want a web browser that remembers every single page I have visited (#) and then lets me search them. Then someone could write a spaced reminder thingy for me - spent more than 5 minutes on a web page did he - he will want to refresh that page in 2 weeks and then 4 months.
Yes, knowledge bases are excellent for clearly defined study efforts - like y'know, university, but for the rest of life, explicit note taking is a cost that we need some activation energy barrier for.
Put it this way, once upon a time I had a study book for a new programming language, and i took notes of interesting examples on a ring binder. But the last time I learnt a new language I just relied on Google finding me the relevant StackOverflow pages - my cost/benefit line had changed.
(And notes just got dumped into a text file.)
(#) Ok maybe not those pages