Why? Github is already owned by Microsoft, who are deep in with OpenAI. And what worth would a Github-clone even have for the world? It's not like there is any important innovation left in that space at the moment, or are there any?
On the other side, thinking about, if all the AI-Slope is moving to their own platform, it would be a big benefit for Github. And maybe this is their real goal? To let Github continue being a source of good high quality human-maintained training-material?