Hello, here is my opinion/research:

The conventional way of cooking rice in a rice cooker works with the lid closed. Anyone who has ever boiled cow's milk in a pot knows that it quickly boils over. If rice pudding is prepared conventionally in a rice cooker with the lid closed, the milk would spill out of the rice cooker.
Another problem: to prevent rice pudding from burning, it must be simmered over a low heat and stirred constantly. Unfortunately, you cannot set the temperature of the rice cooker manually on all appliances.

Rice cookers are ideal for perfect dry rice, but it's better to stir rice pudding by hand and keep it under control as if it were boiling over, it would foam.