If they open sourced their core site, how would they make any money?
Considering the amazing value Github provides for the IT world, I really don't care if they release their code.
Isn't it enought that they have revolutionized development workflows, project hosting and made contributing and collaborating so much easiert?
(to be clear, GH wasn't the first site of it's kind, but the network effect of having one site that that basically every developer uses daily -and be it just via one of the documentation site on GH pages- really was revolutionary)
But I remember it as always clumsy (even before they got bought and started the ad craziness), and only a small subset of projects was on Sourceforge, in my experience at least.
Even if their entire stack was open sourced, GitHub would still be a profitable company simply because it's GitHub. They're hosting hundreds of thousands of repos on bare metal and providing tools around those repos allowing for the maintenance of a community - that's why they are making money; not because of some secret sauce in the code. Otherwise, GitLabs would have eaten their lunch by now.
I could definitely be wrong, and they do have 8ish pages of projects they offer up themselves, but so many are just meaningless dumps of one-off projects.
a) Have to include a lot more documentation
b) Be a lot more paranoid about best practices, and writing generalizable code even if it doesn't fit their particular slice of the market
c) Never have the chance to use a closed source solution for part of the problem (e.g. no we can't have half our app actually be a series of Oracle specific stored procedures, or buy a UI package for $20,000 rather than use a heavily modified version of Bootstrap).