This move doesn't worry me, as I'm sure Microsoft would look to do something easy to calm the nerves of people who worried about Microsoft's acquisition. The cynic in me sees this as sweetener for Microsoft's later moves to integrate GitHub with Microsoft's developer tools, which will infuriate me along with millions of other developers.
This was always one of the core worries about GitHub and Microsoft. Microsoft will not leave GitHub alone. It's too important to developers, and no matter how much they say "we won't touch GitHub", nobody (rightfully) will believe them.
I guess it only counts open source projects, but still that's a lot of data.
Afaik I saw the data set was updated weekly.. afaik it's maintained by GitHub.
B2B revenue is huge compared to anything you'll get from the few hobbyists who are both able and willing to pay for this kind of service.
I know several people I worked for or did business with that paid for Organization accounts, from Team to Enterprise.
I didn't opt to pay for GitHub until I needed to host some private config files in Git, and at the time (maybe a year, year and a half ago?) GitLab wasn't in as great of shape as it tends to be now: for me, it was slow, unreliable, and sometimes just felt "off" in ways I can't really quantify. I already used Github for open-source work and at my day job (and had been using it at work for years), so I paid up (given the alternative, with GitLab not being what I was looking for, was to pay up and host a Gitea instance, or use BitBucket, which was a complete non-option for me).
These days GitLab seems to be a lot more stable and able to handle day-to-day workflows, but GitHub still has the community factor, so all my public repos and forks live there. It made sense to continue to keep my private repos next to my public ones, so when my annual subscription renewed, I was cool with it.
Migrating fully over to GitLab/Gitea/flavour-du-jour is something that's perpetually on my "TODO: investigate" list, and never actually gets done, because despite any minor gripes I may have with it, GitHub tended to "just work", and it "just worked" ~$80/yr worth.