When The Simpsons first hit television screens in 1989, it was clear who the star of the show was. The family(?) animation placed pineapple-headed Bart at the centre of its early episodes, and it didn’t take long for catchphrases like "Don’t have a cow, man" and “Eat my shorts!” to ingrain themselves in the minds of viewers.
But after the third season, then-writer Conan O'Brien presumably grew tired of repeating the same old tropes and basing the majority of the episodes around the four-fingered alternative to Dennis the Menace, because he then led the charge to shift the show's focus from Bart to Homer, increasing the range of social scenarios and activities from the schoolyard to the wider adult world.
After all, there’s only so many times a reasonable person can laugh at Bart saying "¡Ay, caramba!".
https://www.yahoo.com/entertainment/22-seasons-south-park-learned-120000130.html
But after the third season, then-writer Conan O'Brien presumably grew tired of repeating the same old tropes and basing the majority of the episodes around the four-fingered alternative to Dennis the Menace, because he then led the charge to shift the show's focus from Bart to Homer, increasing the range of social scenarios and activities from the schoolyard to the wider adult world.
After all, there’s only so many times a reasonable person can laugh at Bart saying "¡Ay, caramba!".
https://www.yahoo.com/entertainment/22-seasons-south-park-learned-120000130.html