They are doing it, but there's no profit incentive. Github is a bit of a special case because of their commitment to OSS and the broader engineering community, but the moment a downturn occurs and MS takes a harder look at P&Ls, you better believe that's on the chopping block.
The public sector is exactly where you need things that are important to society but don't make money.
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.
https://github.com/advisories
Note that many of these entries start with GHSA not CVE.
Agree that the military budget should face large cuts too, unless I guess a major war breaks out.