>>3617667>difficultlyDifficulty's not the right idea, it's focus. There is just simply little concern for making cute character designs, the focus is almost solely on comedy, and the art style reflects that. Bart, for example, was NEVER intended to be cute, just look at the original design on the Tracey Ullman show. Later, the Japanese just happened to find his personality endearing. This was never the original intention of the showrunners.
I will fight you on Gumball's design, though. He was made to be cute, and is, but he's never as cute in the show as he is in a lot of fanart because cuteness is just not the primary focus of the show.
You're in luck, though, because the new generation of Western animators grew up with anime and are now used to pleasing, cute character design in tandem with comedy, and intentionally ugly stuff like Family Guy is being phased out.
I still curse that buddy of John Mulaney's for making Big Mouth, that crap sets us back at least 3 years.