This is not a magical achievement, github is solvent and its business model is solid, give the same amount of users to any other service and it might collapse. Any service has to scale and the more users it has the more costs it incurs, nonprofits are a risk, the moment they run out of money, the service collapses.

If it's not a magical achievement, then surely competitors could replicate it too.

Of course you can't put a million users today in a service used by a thousand yesterday, but I don't buy the "non-profits don't scale" argument. If that were true, we wouldn't have Wikipedia either.

Replication is not enough, Competition only wins if it offers lower cost or better service (or intolerable service if free), While yes, the userbase is essential, you're still ignoring the reason why the userbase is there in the first place services before github existed and github is the one that ended up winning, competition cannot just offer a better ethical stance and its not even that, since github itself is not doing anything criminal, it's simply aligned with microsoft, so the ethical stance is "I don't like AI" and "I don't like microsoft", that is simply not enough of an offer to make the entire userbase switch. the only way you could is if github decided to throw all of its userbase like bitbucket did, and given that its name is git, I doubt they'll ever do that.

To clarify, I think it's fair to say "I use GitHub because I don't think MS is that bad" (I disagree, but it's at least a consistent view.)

I only take an issue with "I think MS is morally reprehensible but everybody uses it so I'll keep using it too" because it's a self-fulfilling prophecy. Most people looking for code hosting will use whatever they first run into, so when you choose a host for your project you are also directly channeling users towards said host. It's your responsibility to pick a host for your projects that isn't evil by your standards, whatever those may be.