Those folks that I listed are the “late night kings” on the networks, but none has the viewership of Gutfeld.
If you were unfamiliar with Gutfeld - you asked who he was - then you’re out of touch with popular culture. This is not an insult but an observation.
I can’t name a single hit by Taylor Swift, Lizzo, or Katy Perry, but they’re out there, so I’m also out of touch with pop culture. 
You got me. I am out of touch with the idiocy that is broadcast on FOX and all the idiots Murdoc hires and subsequently fires when they get the network into deep financial shit.
Gutfeld is one singular late night talk show host representing the far right, maybe the only one in of note in that category, as compared to the list of several 'late night kings' who appeal to pretty much the same left leaning audience. I think you can understand why Gutfeld's viewership is unimpressive. The same reasoning applies to FOX News viewership stats.