I do not work at MSFT but I don't feel that I need insider perspective to understand what's going on. GitHub is being managed the way other services get managed once they're bought by big companies. Initially fine, then starts to decline, then eventually craters. Everything becomes the numbers game.
Microsoft, Oracle, VMware, CA (where software goes to die), Salesforce, the list goes on. Every once in a great while there's a good M&A team that doesn't fuck it up but that's sadly rare.