MS monetizes enterprise development tools, but makes tools available for free to single developers/small shops. Again, they see it as in their interest for people to develop content for their platforms. And there is nothing wrong with C as a modding language. The vast majority of games are written in C++. Microsoft's version, C#, is very similar to Java. The only issue is that you are dependent on the API.
Actually, with Visual Studio everything compiles to the same runtime, no matter what format it's written in. You could write in Visual Basic while someone else writes in C++. The compiled libraries are shareable.
MS likes to get VS into individual/small shop hands for the same reason Apple started putting their computers (at a loss) in the hands of Schools/teachers back in the late 70's: Kids who learn on a specific product tend to stay with that product later in life.