Why do the pigs in Animal Farm become more and more human like towards the end of the book?
Orwell was obviously using the farm to stand in for the Soviet Union, Napoleon for Stalin, etc. And the point of the pigs becoming more and more human-like was meant to show the evolving relationship between the Soviets and the rest of the Allies during World War II. Just as the revolution that began with great hope for changing the lives of the average Russians changed over time and was co-opted by the Soviet leadership into a system that robbed the average man of nearly everything in order to keep a group of administrators and autocrats in power and wealth, the pigs on the farm demonstrate this shift in their becoming more and more human.
By the end of the story, the "lower animals" can no longer tell the difference between the pigs and the humans and this correlates to the alliance between the Soviets and the Allies at the end of WWII where the Allies agreed to basically look the other way as Stalin murdered millions of his own people and were complicit in this action.