> the best way to ensure that you have the largest possible number of eyes on it
Potentially. Or it means that your work becomes diluted and lost in the ocean. The Instagram problem: many eyes but they're focused on a few targets. Most 'normal' posters will have only a handful of followers and a few 'likes'.
If you have a specialised codebase, say something to do with astrophotography, putting it on Github isn't really going to launch it into the mainstream with thousands of contributors who just stumbled upon it. People who need it will find it by other channels regardless of where it is hosted.