Why knowledge is not centralized?

What is your question? You are currently in charge of your knowledge consumption. What is preventing you from building a personal knowledge base?

I'm currently trying various tools for managing information and plan to build something custom for myself. The current tools I'm using are raindrop.io (bookmarking/searching), notion.so (note taking), keybase (file sharing/note taking), and maybe one more but I'm forgetting.

There are tools to manage your consumption and knowledge habits if you look for them and none of them require a centralized knowledge base.

Who will be in charge? Imagine something like Wikipedia or Stack Overflow. They work but they are not perfect. (Or in the other extreme 4chan and Yahoo Answers)