Fox news viewers are quite elderly, average age of 68 as of 2017. Older people consume news and media primarily through their TV and newspapers. Younger people more through their PC and smartphones (source).
With younger people moving away from TV, that means a larger proportion of the TV watching audience will be elderly and elderly people tend to be more socially, politically and economically conservative (source).
So with a graying TV news audience, it's no surprise that conservative-leaning news media would proportionately do better than centrist or liberal news media. People seeking a more left wing perspective have abandoned mainstream TV news and tend to go to specific YouTube channels or news websites (Democracy Now, the Intercept, The Real News) rather than tune in at 9 o clock to hear what Wolf Blitzer, Jake Tapper, Rachel Maddow, Anderson Cooper, Clare McCaskill or John Kasich has to say.