Because it's very interesting and very high quality. Also, from the guidelines of this site: Please don't submit comments complaining that a submission is inap

Because it's very interesting and very high quality. Also, from the guidelines of this site: Please don't submit comments complaining that a submission is inappropriate for the site. If you think something is spam or offtopic, flag it by going to its page and clicking on the "flag" link. (Not all users will see this; there is a karma threshold.) If you flag something, please don't also comment that you did.