I think most times this happens because the description of the project is hosted elsewhere, and github is primarily thought of as a way to host the files for do

I think most times this happens because the description of the project is hosted elsewhere, and github is primarily thought of as a way to host the files for download. I see this a lot with projects that only link to the /releases/ page, especially when the code itself is not open source. Or, they're just too close to the project and the idea that someone would have to read the readme completely slips their mind.