His novels 1984 and Animal Farm, which attack English and Soviet socialism very directly, are taught instead as generic anti-"totalitarian" works.
As David Aaronovitch writes in BBC News Magazine,
[T]here has been a well-established and heartfelt desire on the more moderate left to claim that Orwell was indeed a genuine socialist whose warning was aimed at totalitarianism in general, not at the left per se.
I was reared and schooled by the kinds of leftists who embraced Orwell and taught me that 1984 was about totalitarianism in general, not socialism per se. I even thought of the book as an attack on the Reagan administration, and argued with my (neo)conservative girlfriend about it in high school. A few years later, I was very embarrassed by my easy acceptance of the interpretation I had been taught.
(h/t Wendy McElroy)