Github is not something that most devs use much of the time. It is really there to provide the open source code for the public. Any real dev is using a Git server of their own to share with the team or, if there is no team, they may not even need to have up to date code in multiple locations or they use a simpler method.
Our old software company put out software for 18 years before we ever touched a github account. For someone that is working on something and has not finished or released publicly yet, they might as well hang a "steal my idea" sign on the project if they put it on github. That is a final step and a way to keep the releases up to date for the public, not something that will be used often.