You didn't answer my question though. Why would they alienate half the potential audience by being politically motivated for one side over the other?
Primarily because of the position taken by their editorial board, much of it for political reasons although financial reasons likewise play a major role as well.
The first part of the sentence makes sense and I agree with it. The second part though completely contradicts it. As a consumer, I see many news outlets as democrats first. Reporters second.