Indeed....ands I agree , I think there is a certain exhaustion that has set in as well.
(Though it appears, some ascribe the death of white males as a probable cause, but are now busy papering that over because their mask slipped

).
I just think the election was tiring, I know I am tired, and being on the losing end is even more tiresome. I would guess its both audiences, the victors feel they can rest, the losers just fade out for a while......
Almost certainly there was higher viewership of ALL television news media during the months leading up to the election when people were interested in the election. After the election was over, a lot of that interest no longer existed and viewership of all television news media almost certainly fell off. (
I didn't make that a statement of certainty because I frankly don't care enought to check all the ratings for all those weeks/months.)
And yes, after being immersed in politics almost 24/7 for weeks and weeks, people often do reach the saturation point. I certainly do. So Fox isn't getting nearly as much ratings out of my television viewing as it did a few months ago. I watch enough to see what they're covering, but don't stay with it hour by hour while the same stuff is rehashed over and over and over. I would rather watch Survivor or American Idol or The Amazing Race or a good movie if I am going to watch anything. I'm guessing that is the case with fans of other cable news too.
But that is true of all other media too. I still scan the headlines at Drudge and Breitbart and Huffington Post to see what the news of the day is, and still read enough from various sources to keep up with the current issues. Right now it is all focused on sequester and the ramifications of that. So I inform myself best that I can re those ramifications, but am not interested in hearing the same opinions expressed by commentator after commentator at any source.
So in slow news periods, Fox News, and everybody else, is going to have lower ratings. And if something really special or profound happens, you'll see their ratings, and everybody else's, spike.