Erm, Microsoft are massive. They have lots of customers who have vastly differing needs which generally don't compete with each other.
There are a LOT of Windows applications built on C++. Most games and most intensive applications are C++ based.
Their corporate business customers generally use either C# or VB.Net with a large number still supporting legacy applications in Visual Basic.
Their web customers naturally use javascript/css/html for client-side and one of the managed languages server-side.
So it's not surprising to see them pushing three big languages for their big (and very different) markets.
Microsoft have a pretty good record of supporting their own languages. Visual Basic is still in use today dispite it being terrible. C# is very well supported, and they have a pretty good C++ compiler and toolchain.
IronPython, IronRuby, J# etc were all Microsoft's attempts to "play with the cool kids", clones/forks of existing standards. All died the inevitable death when the next fad came along (see F#).