Keep in mind that a celebrity can send you and me, regular joes, a C&D and we’d likely comply simply because we lack the resources to sustain a challenge in court.

What stops celebrities and organizations from suing South Park creators is likely the opposite: they have money and a legal team.

The same thing happened with John Oliver when he talked shit about some coal mine owner that was notorious for suing people. The mine owner served them from a court that had friendly laws but they were ready. And they had insurance to pay for it.