It's Markdown, not just "a README file". It's designed to be easy to edit by hand and easy to parse; there's literally nothing at all gained by using the JSON file that they have. At all.
You'd be more likely to have a bug parsing the markdown file than the structured JSON. There aren't many tools out there for converting markdown files into JSON and piecing what you want out of it.
Yes, the JSON version is for use in a website or app.