The answer to your question is that George Orwell felt compelled to speak out against the dangers of English imperialism and fascism.
Orwell for our time.
If we go back and study the man himself, we can see that Orwell was an old-school English socialist; politically, he was unabashedly left. He prided himself on his support for the working poor, for freedom of speech and thought, and for democratic, classless societies. Yet, Orwell was staunchly anti-establishment; we can see this in his harsh criticism of the elitist Labour leaders of his beloved England:
“The truth is that to many people calling themselves Socialists, revolution does not mean a movement of the masses with which they hope to associate themselves; it means a set of reforms which ‘we’, the clever ones, are going to impose upon ‘them’, the Lower Orders”. (The Road to Wigan Pier)
While the elitist leaders of England claimed to support the defeat of an imperialist Germany, they essentially turned a blind eye to the excesses of communist Russia. The ruling Labour leaders were career politicians who favored exchanging one form of totalitarianism for another, as long as their power and privileges were preserved.
Essentially, this is what Animal Farm is about: Orwell's pigs (led by Napoleon and Snowball) were thinly veiled caricatures of Stalin and Trotsky. The pigs manipulated widespread anger and dissatisfaction among the animal populace to set themselves up as elite leaders in place of the farmers. The English Labour leaders were like Snowball and Napoleon, only interested in their own aggrandizement and success. For a time, they may have appeared to engage each other in a seeming struggle to secure proletariat rights, but in the end, their only goal was to set themselves up as bourgeoisie leaders over a scattered and divided populace.
In Animal Farm, the animals discovered that they had essentially exchanged one group of oppressors for another. There was to be no democracy, where they would have equal say in how the farm was run; there would only be the prospect of servile obedience to an indifferent and ruthless ruling class.
Everywhere the world movement seems to be in the direction of centralised economies which can be made to ‘work’ in an economic sense but which are not democratically organised and which tend to establish a caste system.'(George Orwell's letter to Noel Willmett)
Twelve voices were shouting in anger, and they were all alike. 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. (Animal Farm)
As with Orwell's Animal Farm, both Coming Up For Air and 1984 were equally controversial. England looked wretched in these novels because Orwell felt that England's leaders were in danger of appropriating totalitarianism for their own purposes. As a socialist in the purest sense, Orwell believed that no government (whether left or right on the political spectrum) should resort to coercion and violence to control the populace.
...there is the fact that the intellectuals are more totalitarian in outlook than the common people. On the whole the English intelligentsia have opposed Hitler, but only at the price of accepting Stalin. Most of them are perfectly ready for dictatorial methods, secret police, systematic falsification of history etc. so long as they feel that it is on ‘our’ side. (from George Orwell's letter to Noel Willmett)
In Coming Up For Air, Orwell's protagonist, George Bowling, also comes to this conclusion. At a talk during a Left Book Club meeting, Bowling has an epiphany: the elitist vision of revolution only serves to benefit a small group while the masses suffer.
I saw the vision that he was seeing. And it wasn’t at all the kind of vision that can be talked about. What he’s saying is merely that Hitler’s after us and we must all get together and have a good hate. Doesn’t go into details. Leaves it all respectable. But what he is seeing is something quite different. It’s a picture of himself smashing people’s faces in with a spanner. [CUA p. 148]
Hitler’s after us! Let’s all grab a spanner and get together, and perhaps if we smash in enough faces they won’t smash ours. Gang up, choose your Leader. Hitler’s black and Stalin’s white. But it might as well be the other way about, because in the little chap’s mind both Hitler and Stalin are the same. Both mean spanners and smashed faces. [CUA p.149]
In 1984, England is essentially Oceania, one of three powerful states which are constantly in conflict with one another. Oceania controls its populace by controlling language and thought. The country is headed up by Big Brother (who no one has ever seen), and he is aided by The Inner Party and The Outer Party in his efforts to keep the Proles (the population) suitably cowed and docile. In the novel, violent means are used by the oligarchic elite to mercilessly subdue any perceived act of rebellion against it. So, the state is all-powerful; it has appropriated all means of production, all intellectual discourse, and all memories of the past for its own nefarious purposes.
Basically, through his three books, Orwell painted a grim picture of what his beloved England could look like if it continued on the path of rationalizing away the dangers of totalitarianism. It was his personal belief that both the Left and the Right were in equal danger of preserving an amorphous state at the expense of the suffering masses. His aim had always been to warn and to educate.