Earlier quoted context omitted.
I don't mean this as a knock on Github, but I'd argue they are a company that lives on selling corporate licenses and enterprise software to companies that don't want everything to be public.
Correct. They earn money off of private repositories... not sure how them hosting public projects adds directly to the bottom line besides the obvious marketing benefit and sticky factors.
not sure how them hosting public projects adds directly to the bottom line
They get a ton of feedback and insight from non-paying users. The usage and feedback can drive both the product and business roadmap for their enterprise offerings.Every developer who enjoys using it for personal or open source is also likely to recommend it to their employer as well. I know I have helped drive adoption in a few organizations.