Ooh, you just more or less described me. What makes working on public things, say, one weekend every couple of months less interesting than not working on public things at all?
Though anyone looking only at my GitHub profile might reasonably think so, I guess.
One thing I'm seeing more commonly is where a group of people create github profiles with a handful of projects that are obvious homework assignments, and then open and close a few issues and pull in some trivial changes to each others' repos in order to put a few green dots on their contributor graphs.
Sad really.
On the other hand a genuine contributor may be working offline each day for months then do a big commit (squashing down the intermediate local history - can't remember the git term for this).
What I think would be good is to instruct candidates to write a cover letter about their side-projects. Talk about each one briefly. With links to online repositories if available (or zip files otherwise).