Maybe "secret sauce" is the wrong term. People ended up choosing GitHub purely because of network effects, I think. But those features are the "lock-in" preventing individual projects from easily migrating away.
If Git repos just "had" wikis, issues, etc. inside them, the lock-in wouldn't be there, so people would be switching between Git hosts all the time—and there wouldn't really be much value in a "git host" at all, beyond what just having a Git dir on your own server, plus a native-GUI Git client supporting the wiki/issues/etc. features, would get you.
Maybe there’s no secret sauce of any value and it’s just pointless github is closed source, like a form of DRM just being used against us cause we’re silly and let it be so even as we aspire to see open source flourish...
If Git repos just "had" wikis, issues, etc. inside them, the lock-in wouldn't be there, so people would be switching between Git hosts all the time—and there wouldn't really be much value in a "git host" at all, beyond what just having a Git dir on your own server, plus a native-GUI Git client supporting the wiki/issues/etc. features, would get you.