Probably because they think they're too smart to just report the news. They are compelled to analyze and comment on it, so that stupid, ignorant, uneducated people like us can begin to understand it.
One of the main reasons that a majority of American voters ARE "stupid, ignorant, uneducated people" is EXACTLY FOR THE REASON that they DO NOT REPORT the news as it actually happens! If they did, the people would not be so ignorant.
But it is all in the plan to keep the voters ignorant, and it sickens me!