It is the very success of Fox News--they pull significantly more audience than all the other cable news channels combined--that gets the left's shorts in a wad. And they can't point to Fox being the ONLY right leaning source as the reason for its success because if you add all the left leaning channels together, they can't combine to pull the same audience in almost any time slot.
It does have to be galling for those who are convinced that the left is the path of all that is righteous and virtuous and good and conservatism sucks. So they invent all manner of theories that only the gullible, ignorant, stupid, and brainwashed could possibly find Fox interesting.
Fox (and all the other cable news programs) does attract political junkies who are more interested in politics than they are probably interested in most other domestic issues. People who don't watch a lot of political news but look to other sources for news probably do have an edge on specific information about many domestic issues.
I'm pretty Fox News watchers would accomplish themselves quite well on any survey restricted to political issues, personalities, events, etc.
Meanwhile, the beat goes on to demonize Fox for no other reason than it continues to be politically incorrect. And it is for that reason that I watch it more than any other.
One of my favorite political cartoons: