You've had some pretty cynical answers here, all of which are true, but there are further reasons.
You are more valuable to your organisation if more people understand how awesome you are. They can seek you out (through whatever structure the company has) as a contributor to projects most in need of awesomeness. They can plan projects knowing what people are awesome in what ways, that they never would have realised were possible otherwise. General knowledge cannot come solely through chain of command, there needs to be some cross-talk.
Visibility is somewhat reflective because of the process of gaining it. In making yourself visible, as opposed to your manager just hyping you on his own, you are involving yourself in the organisation and probably learning more about other people's awesomeness. Then you will make better decisions.
A workplace in which people are mutually aware of what each other can do is not "polluted", and a workplace in which you sit in a bunker, speak only to your manager, and churn out great code without any relation to the organisation other than what your manager sets up, is not "pure". The latter is one way to work, but it's not the way your manager wants you to work.
So, gaining some visibility in the organisation and especially"taking up stuff" are important parts of your professional development. There is an important political element, but it might not be as bad as you think and you won't find out unless you engage with it somewhat.
