Why? Because politics has increasingly become about campaigns and candidates talking to people who are already paying attention to what they are saying. Again, why? Because those high news consumption folks also happen to be — surprise, surprise — the sorts of people who turn out to vote. And where do those people tend to reside on the political spectrum? On the far left and the far right, of course. Independents? Not so much.
Think back to the 2012 election. Did President Obama win a second term because of his capacity to persuade undecided/independent/unaffiliated voters? Nope! Mitt Romney won independents 50 percent to 45 percent. At the heart of Obama's victory was his team's understanding that the key to winning wasn't convincing independent or unaffiliated voters but rather ensuring that everyone who was already for him (or would be for him if they were contacted in the right way at the right time by the right person) turned out.
That wasn't a new tactic. Making the presidential election a battle of the bases was executed to perfection by George W. Bush in the 2004 campaign. Obama's 2008 campaign was such an overwhelming win that he romped among his base, independents and everyone else, but the pillars of his victory were more-unified support among elements of the Democratic base, such as black and Hispanic voters and young people.
This battle of the bases is only likely to escalate in 2016 as advances in technology make it harder and harder — and more and more expensive — for politicians to reach people who aren't already on their side or, more accurately, paying much attention.
Such a "base" campaign will likely grow the ranks of so-called independents as they feel ignored and unappreciated by the two major parties. Of course, until independents start paying more attention to politics, they don't have much room to complain.