There's a profit incentive: GitHub sells its services. The free stuff is an advert. At any rate, even if they give it away for altruistic reasons, Microsoft is

There's a profit incentive: GitHub sells its services. The free stuff is an advert. At any rate, even if they give it away for altruistic reasons, Microsoft is a sustainable going concern that brings in more than it spends. It can afford charity. The US government isn't and can't.