We know the beautiful theory. Show me something easy to onboard and use. I've learned no less than 500 separate tech pieces in my life, Nix and any others will have to make it worth my while in the first 10 minutes.
If you've learned more than 500 things, why does the 501st need to be so much more special in order to be worth your time?
Because most of those that I have learned were bad at onboarding, and you do get sick of it after a while. I've improved no less than 25 projects' README's (sadly all private / corporate so I can't even advertise myself that way) by removing 50 lines of semi-useless prose and replacing them with 2 paragraphs 4 lines each and one small code block as a usage example.
So TL;DR -- because most programmers can't describe a use-case if their lives depended on it.