There's a reason GitHub is the largest service lol

You need to sell services based on their advantages rather than the politics. The reality is, github allows projects to be very easily migrated to other services anyway.

Using something because it's open source isn't helpful at all if it doesn't work with your workflow easily

Productivity is more important to the success of open source than anything else.

I know this, because a project of mine died because we wasted too much time on infrastructure

Developers don't need access to the GitHub source to do their job, and there is no advantage to anyone.

In fact, if they distribute the code, it simply reduces the incentive for Microsoft to improve it, and the only ones who will step are, are shit companies like Oracle