They're not charity. They have right to do whatever they want with their source.
Copyright is a government granted monopoly on intellectual property, not an inherent right. What needs to happen is extreme reform (or outright abolishment) of copyright. Though that's basically a pipe dream right now
Not sure on the effort required. I checked GH (not a Microsoft company...) but couldn't find the source code.
People and organizations can act within their rights and still be detrimental other people, organizations, and communities.