I cannot comprehend why GitHub chose to let people define the form elements in YAML (!) instead of simply allowing <input>, <select> and <textarea> in Markdown.

I cannot comprehend why GitHub chose to let people define the form elements in YAML (!) instead of simply allowing <input>, <select> and <textarea> in Markdown. One of the most beautiful aspects of Markdown is that it supports HTML. It's trivial to allow only a minimal set of attributes, like `required`.