The animals undertook the revolution in the first place to improve their lives. They were exploited and brutalized under Jones and the humans, and they thought that by controlling their own lives, they could make them better. At first this was the case. But as the book develops, Orwell shows how as Napoleon gradually arrogates more power and privilege to himself and the other pigs, the other animals on the farm return to a situation that seems as bad, or even worse than the one they rebelled to change in the first place:
They were generally hungry, they slept on straw, they drank from the pool, they laboured in the fields; in winter they were troubled by the cold, and in summer by the flies. Sometimes the older ones...tried to determine whether in the early days of the Rebellion, when Jones’s expulsion was still recent, things had been better or worse than now. They could not remember.
So by the end of the book, the animals face grueling labor, very strict food rations, and brutal punishments. Despite failing to deliver on the promises of Animalism, Napoleon is able to maintain power through a combination of fear and information control. Through Squealer, he cultivates a cult of personality for himself, embodied by Boxer's mantra that "Napoleon is always right." He creates a constant sense of emergency by always claiming that Snowball is attempting to destroy the farm in league with the humans. Perhaps as important, he develops friendships with humans on other farms. The animals' oppression, and Napoleon's corruption, are complete by the end of the book, when the animals witness a poker game between the pigs and humans from an adjoining farm:
No question, now, what had happened to the faces of the pigs. The creatures outside looked from pig to man, and from man to pig, and from pig to man again; but already it was impossible to say which was which.