As far as I'm concerned GitHub is free to handle the licensing of their software however they like, but this opens up an interesting thought experiment:
We now have at least two companies making significant Chromium-based editors, one is Adobe and the other is GitHub.
One of them is developing the core of their editor technology using a fully open-source model (hosted on GitHub, naturally) under a well-understood and widely accepted license, the other isn't (or at least isn't currently planning to).
2 years ago, who among you would have guessed correctly that the one whose editor was open source would be Adobe's?
We now have at least two companies making significant Chromium-based editors, one is Adobe and the other is GitHub.
One of them is developing the core of their editor technology using a fully open-source model (hosted on GitHub, naturally) under a well-understood and widely accepted license, the other isn't (or at least isn't currently planning to).
2 years ago, who among you would have guessed correctly that the one whose editor was open source would be Adobe's?