Because it's a puff piece for Usersnap's feedback service. Bourbon, Inuit, and Compass would probably be worth mentioning as well. Admittedly geo-bootstrap was new to me, so thanks for that :) (Rather, pass the eye drops!)
http://bourbon.io/ A simple and lightweight mixin library for Sass
http://inuitcss.com/ a powerful, scalable, Sass-based, BEM, OOCSS framework
http://compass-style.org/ Compass is an open-source CSS Authoring Framework