Facebook has something like Instagram for everyone to share and talk about photos. However, GitHub's integrated gisthub.com is not convenient to share and talk about code with others. For one, GitHub's notification system does not allow for following gist publications. On the other hand, the "GistHub" is not intended for sharing things broadly and publicly as, for example, Twitter is.
In other words, programmers and scientists mainly share on their blogs, publications, and source code repositories. However, none of these media are really friendly for broadly social discussions.