The other animals do not protest against Napoleon's dictatorial decisions because they lack power and knowledge, and because they are afraid of his brute force that is carried out by the "fierce looking" dogs who constantly surround him.
As an example of Napoleon's despotic control over the other animals, in Chapter 7 of Animal Farm Napoleon orders the hens to surrender all their eggs, which will serve as payment to Whymper (with whom he has made a contract of four hundred eggs a week). In payment for the eggs, Whymper will provide enough grain and meal to keep the farm running. Hearing this, the hens clamor and protest that removing their eggs from them is tantamount to murder because the spring sitting produces the next generation. They launch a rebellion of sorts:
Led by three Black Minorca pullets, the hens made a determined effort to thwart Napoleon's wishes. Their method was to fly up to the rafters and there lay their eggs, which smashed to pieces on the floor.
Napoleon acted "swiftly and ruthlessly" by cutting off the rations to the hens, and pronouncing that any animal who gave the hens even so much as a kernel of corn would be put to death. "The dogs saw to it that these orders were carried out." Of course, several hens die of starvation, so after five days the hens abandon their protest. Whymper receives his eggs after this incident, and his truck arrives every week afterwards.