Earlier quoted context omitted.
What happened to people who can write successful products but not yet been open sourced? This happened to John Carmack, Jamie Zawinski. They are probably too busy in making stuffs work then writing answers on Stack Overflow or committing code to GitHub.
Some people do both. Why gamble on someone who won't show any of his work when you can just pick someone who does?
But if the code has copyrighted issues, then how can I show publicly? I usually have a copy of repository for my past projects and I don't mind to show it to people who interview me.
Also I think if I need to put code on GitHub, it has to be some software for more generic tasks.