My two cents? Because they have based their entire business and clientele around an open source piece of technology. Their contributions back to the community which gave them the core of their company feels... anemic.
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.
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.