I imagine the vast majority of employers would be pretty pissed if the vast majority of programmers shared their private code, and some might even wish to take

I imagine the vast majority of employers would be pretty pissed if the vast majority of programmers shared their private code, and some might even wish to take legal action. As an employer interviewing and hiring candidates, one should respect and expect this confidentiality to be exhibited and adhered to. For example, I build things for clients that are proprietary to their businesses. Some things are publicly accessible, like marketing pages, but the real stuff is locked behind employee-only auth. Other things run entirely on internal networks, and can't be accessed from the web. They would be rightly upset if they discovered I shared their code with a third party, or placed it on Github. Moreover, just because Github exists, doesn't mean programmers should feel obligated to "participate". Outside of developers who maintain or participate in truly used projects, it's mostly noise. The only exception I can agree on is looking at issues a candidate has reported to gauge their depth of understanding, clarity of communication, offering of solutions, and other such valuable insights.