I was that way when I was younger, I love it now, but for me King of the Hill was too "serious" or realistic, it's less absurd than other similar shows like the Simpsons, the plots are usually more like something that could happen to real people, and the comedy style is drier/more subtle. I have friends who never really got into it when it was newer because of that.

Also having family from the southern/midwest US there are aspects of the characters that tie into cultural tropes that if you aren't familiar with wouldn't appreciate as much, whereas Simpsons and Futurama have less specific references to US culture more based on Hollywood and political history of the US. For example my grandma who was born in Nebraska and has lived around the south most her life loves King of the Hill after getting into it not too long ago and isn't so much into The Simpsons.