The company I work at "supports" Linux in the sense that you're allowed to use Linux but then you're essentially on your own when it comes to solving problems. I asked why there's no proper Linux support and the short answer was "it's too much trouble". The long answer was "don't ask. I don't want to get into it".
So my guess is that setting up company wide policies and support for Linux is significantly more work than it is for Windows or Mac.