Kudos to MS
Not their biggest fan, but good to see they are chipping in.
As to why... it is easy to deploy alternative open source packages on Windows. If it turns out to be leaky and lets in threats, MS is left picking up the pieces. A la Java on Apple if you recall Flashback (I specially recall Apple was clueless at first helping their users, but it was still Oracle's turd that opened the door).
So hardening low-level, high-usage, OSS programs liable to be put on Windows probably lowers their own vulnerability.
Regardless, good of MS to help out. And I note Apple's absence in CII. Not like they use much open source stuff themselves or have any cash to spare, eh?