I have a two word answer: Intellectual Property. Not everyone is an accomplished Open Source publisher, nor should that be a requirement for employment. So what existing project do those candidates point the interviewer at? Someone else's IP? And then the hiring company is obligated in self-defense to make sure that it's not someone else's IP, lest it end up in someone's hard disk accidentally and get discovered in some otherwise unrelated audit? No. Thank. You. Keep your own code to yourself.
Now, you might point out your own code with some URLs and they may take a look at it. But that's not the same as making it part of the interview process.
I have a two word answer: Intellectual Property. Not everyone is an accomplished Open Source publisher, nor should that be a requirement for employment. So what existing project do those candidates point the interviewer at? Someone else's IP? And then the hiring company is obligated in self-defense to make sure that it's not someone else's IP, lest it end up in someone's hard disk accidentally and get discovered in some otherwise unrelated audit? No. Thank. You. Keep your own code to yourself.
Now, you might point out your own code with some URLs and they may take a look at it. But that's not the same as making it part of the interview process.