They are a choice. The author even mentioned Bitbucket. The fact that Github has become the dominant player doesn't make it not a choice. There is no one preventing a competitor from emerging and working to compete with Github (the same way Git emerged and enabled Github to exist in the first place). Being frustrated that people default to Github doesn't mean the choice to use something else doesn't exist. It does, most people have just decided not to.
They are a choice. The author even mentioned Bitbucket. The fact that Github has become the dominant player doesn't make it not a choice. There is no one preventing a competitor from emerging and working to compete with Github (the same way Git emerged and enabled Github to exist in the first place). Being frustrated that people default to Github doesn't mean the choice to use something else doesn't exist. It does, most people have just decided not to.