Nuance requires representing uncertainty and is higher complexity from accounting for multiple special cases. Placing more cognitive load and attentional demands on receiver.
Human communication is lossy and decoding can be non-trivial inference. Given that everyone comes with differing priors, the more finer grained and complex details are required in reconstructing message intent, the more likely it is to be misconstruected. Failing to attend to a single core detail can rend meaning.
At scale the chance for errors to propagate without correction increases.
Getting rid of fine grained details and communicating a lower entropy message inline with a crowd's biases also ensures it's more likely to survive in a form close to original intent. A good manipulative orator focuses less on truth or content and more on minimizing mismatch between receiver mental states and orator's directional preferences.