Repositories are public for a lot of reasons, a lot of which are not "I want to show this off to a potential employer". Let me give some good reasons, that's not an exhaustive list.
- It is the default.
- Free private repos are new and no one is going back and making things private.
- If you are working with someone it is many times easier to make it public.
- You want to share code with someone, public is easier than making them a collaborator.
Honestly I don't think a lot of people, if any, are reading the stuff I have on GitHub.
