[pron]

Sure, which is why it is sometimes useful. But people who make Java libraries that are production quality, usually don't forget to publish, and if they do, they are quickly reminded to do so. I am not aware of any production quality Java library from the past five years that isn't on Central/jcenter etc.. Older ones aren't on GitHub, either. In fact, supporting sourceforge might be more useful than GitHub, for that reason.