That's probably because for daily tasks we have much better tooling in Windows already that doesn't require us to use the command line and interactive construct it. I can easily administer the configurations of thousands of computers through AD, for instance, and while I could use PowerShell to do so, using ADUC is just easier most of the time.
If you do a lot of work with Exchange though, you'll probably end up using PowerShell much more, because the web UI for it is not so great.
No matter what you think of the specific implementation, a lot of PowerShell's ideas are good ideas. Unfortunately UNIX culture is such that they'll probably never implement any of them.
