Because of things like this:
https://www.youtube.com/watch?v=UnoTelwXuww
http://vimeo.com/116850790
https://www.youtube.com/watch?v=JCCXspvxP_E&feature=youtu.be
https://www.youtube.com/watch?v=Evzx18mI6cg&feature=youtu.be
https://vimeo.com/121645397