All your BASE
Once employers started requiring developers to publish a portfolio on github it became attractive to the likes of MS.
Once MS started changing the direction of github so as to monetize it then the environment becomes ripe for someone else to spring up and compete with github for those who remember MS's many abuses.
Nothing here is suprising beyond the acceptance of developers to allow a third party to hold their IP which previously was protected by not only the law but also direct control by the developer of whom got to know it existed.
Personally I always preferred completely controlling what I owned rather than allowing third party "accidents" where my work could be stolen, alteast my way I knew exactly who I had given access to.