To address #1, there should be simple videos like “how to improve docs in 5 minutes?”, similar to this.
Like this? https://youtu.be/ZpH1ry8qqfw. And it’s only 2 minutes 
But why can’t we have documentation as the one in numpy? Many documentations fail to have a list of their functions and what type of parameters it should have.
The amazing Documenter.jl automates that process, so people who use it can have an API page. Example: Home · FlameGraphs.jl (click on the “Reference” page for the info you were asking about).
So the answer is, we can, it just takes people willing to contribute. Sometimes people expect the main programmer to contribute the docs, and many do, but
- sometimes the person who created something is not the best person to introduce it to a newcommer
- writing documentation is not easy, and people who are good at coding may not be good at documenting (and vice versa)
- to anyone who feels annoyed that the documentation is bad (and it often is): keep in mind that most code is posted for free. If someone gives you one present, it’s not fair to ask for a second present. It’s great if they give it freely, but contributing docs is a way for the entire community to repay the generosity of those who donated their time to write & maintain the code.