Why do we still read a 70 year old book written about a country that no long exists? What does it offer the modern audience?
As an allegorical fable, the history of the start of the Soviet Union is easily accesible for people to understand. People who read this story can look to how propaganda is used to control others and thereby, look to propaganda used today to check for parallels. It is important to always see if the patterns of history are repeating.
It is also worthwhile to read as a story to see how a naive narrator is useful to show irony. Orwell's narration leaves the reader outraged; we want the animals to see and get what is happening to them, but we can't, and when we get to the end of the story, we are always left sad.