The pigs take over running the farm. Why does this seem natural?

Old Major was the original leader so animals simply related leadership to pigs.Once Old Major dies, Snowball and Napoleon use their intelligence by controlling the other animals. Since the other animals were not as smart, they took advantage to be named leaders and manipulate the other animals. The other animals had no idea of this, so it was easy for the pigs to do this and the pigs also lied to them, they really knew how to take advantage of the others weaknesses.