While private repos are usefull, I do not think that is tangled's main proposal at all.
I am just thinking you do not like tangled because you don't use the social features of github and so don't see the point here. I can understand that, but then tangled is just not for you ?
And yeah ATProto is not the next thing, but IMO having a portable identity and services that can act as "one big single app" are requirements for a modern social protocol to do applications like Twitter,Instagram, and github's social features for example, ATProto is just the one that does it better imo for now.
But again since you are always bringing on private repos, I think tangled is just not for you since the ATProto model is for open data and so fits open source projects really nicely I think.