They make an even bigger cartload of money on consoles, and OpenGL is not on the console technology stack. They want the least effort path and DirectX is that path (for XBox and PC's). PC's are an afterthought in games nowdays more and more, consoles being their primary market.
The other platforms wont ever take off without OpenGL on them thereby giving access to all 3 platforms BUT that wont include Consoles until they can get the API's onto that platform too.
Consoles is the main driver now and Microsoft owns that market with DX.
This comment was edited on Jan 28, 15:16.