Or do the opposite. If Microsoft decides to make private repos on GitHub free, I can see VERY big issues for other players. I suspect more people use GitHub alternatives for cost reasons, rather than ideological ones.
When Microsoft shutdown their competing product to GitHub, I think they had like 200 active users. Compare that to GitHub, which had millions of active users. Maybe this is the same with private repos. That is, the number of paying GitHub customers is an order of a magnitude more than free VSTS customers.
I really think Microsoft wants what Amazon has and if they can funnel GitHub users to their cloud service, this acquisition will become a no brainer. Plus, the data that GitHub is able to gather from issue conversations, code reviews, etc. may well prove critical for ML/AI research, that can help Microsoft develop intelligent software tools.
All of that is free for up to five users and it’s all private.
[1] It's only for public projects with a license that doesn't prohibit Google from mirroring it, and only for projects Google depends on.