Comment by NicoJuicy

Microsofts decision to opensource is not suddenly.

It has actively been pushed by some of Microsoft's evangelists (Phil Haack (ex employee, works at github now i think) and Scott Hansselman to say the more popular names).

I believe they got some playfield to do things and now the community has more and more impact (eg. Nuget and software like myget which is based on Nuget (Nuget for Enterprise))

Also, the CEO isn't Balmer anymore, that probably helps to.