I agree with you here. I doubt Microsoft is committed to losing money on a product.

There could be a direct (selling subscriptions / additional addon products) or indirect (marketing dollars, community goodwill, 'mindshare) profit motivations.

I think Microsoft sees this as a way to get into businesses that would have never entertained a relationship with them. When those github enterprise contracts come up for renewal, I expect large discounts for trying Azure and other Microsoft products to come with them.