All this started long ago. Roslyn has been in development for a few years and that was still under Ballmer's leadership. Also many of the other things they're unveiling and open-sourcing now started way before Nadella took over as CEO.
But my guess would be that Ballmer stepping down was sort of symbolic in this regard. With a new CEO it looks more like a "new Microsoft" doing all these things.
All this started long ago. Roslyn has been in development for a few years and that was still under Ballmer's leadership. Also many of the other things they're unveiling and open-sourcing now started way before Nadella took over as CEO.
But my guess would be that Ballmer stepping down was sort of symbolic in this regard. With a new CEO it looks more like a "new Microsoft" doing all these things.
Just because they were working on it before doesn't mean that the plan at the time was to open-source those things...
They couldn't have done it that fast. They just couldn't do it while Ballmer was there - not after his anti-OSS rants.
And he knew it.