Without getting into the issue of whether Gutfeld is funny or not -- to each their own -- I'll actually address the question posed in the thread title.
The answer: Because his political commentary is sharp, believe it or not. I find that Gutfeld often conveys his opinions in an effective, sharply satirical fashion, using metaphor to great effect. Agree with him or not, the man knows how to make a point and drive it home in way that infuriates liberals. Dennis Miller often can't articulate his points of view because 1) he hasn't thought them through or 2) because no one can figures out what he's talking about. Gutfeld slices to the point with simple (perhaps too simple at times) relevant analogies, making an opposing point of view seem ridiculous. You don't have to agree with his views. You don't have to laugh at his jokes. But consider that FoxNews not only gave him "Red Eye," but built the increasingly popular "The Five" talk show around him (and he has written a few books besides). So despite his often sophomoric, raunchy schtick, there is substance there. That's why Fox has given him such a "monster push." Whether Gutfeld is funny or not on Red Eye isn't the point (although his myriad guests often are). Espousing conservative views without coming across as some pompous, stuffy William F. Buckley Jr. type IS the point. Liberals have been poking fun of conservatives for DECADES in the mainstream. For the last several years, hidden in a late time slot (especially in the East), there is a show where conservatives do the poking ... and IMO it's funny shit. :2 cents: