In an interview with NPR, Trey Parker explained, "We always had this thing where Cartman's mother was so sweet—she was always so sweet to him and giving him whatever he wanted. And I don't know if it's worse in L.A. than most places in the country—I hope so—but [we've met] so many parents who were just so desperately trying to be friends to their kids. And it was the thing we really picked up on. And it was just like, 'These [people] are making these really evil kids'".
At the end of "Tsst", Cartman's mother bribed Eric into watching an opera with her when he was otherwise going to work on a science project.