alt Hacker NewsI don't see any reason that GitHub should use rel="nofollow"
Github only has authority because people put their shit there; if people want to point that back at the "right" website, Github should be helping facilitate that, instead of trying to help Google make their dogshit search index any better.
I mean, seriously, doesn't Bing own Github anyway?
Perverse incentives strike again! Websites that allow links in user-generated content are spammed with user-generated spam links to improve SEO of spam sites, which hurts the site's own reputation because most of the links on it are spam. To avoid this, all sites use nofollow.