Funny, I thought github was a code repository, not a personality type...
real engineers know that most good code isn't on github and never will be
Irrelevant. Fact is, having code out there makes it easier for prospective employers to get a feel for you, there's no way around that. No one said it had to be the best code or all the code.
Now, if you are working your ass off on proprietary code and write absolutely no code outside of your work, then you won't have it. That's understandable, but doesn't change the fact that it makes it harder for someone to figure out what you can do.