It isnt, but then, a History curriculum has to pick and choose certain things. I can recall doing 1066, the Tudors, and WW1 + 2, because these are seen as defining features in English/British history. We also did the Holocaust, because...well, it's the Holocaust, it needs to be taught.
As for the war of Independence, firstly, I'd say that we weren't taught anything about British Imperialism at all through Primary and Secondary school.
It might be because the politics of this time is pretty damn complicated (I did a module on the rise and fall of British power, at university) so any primary schoolers or high school students would get bored with it pretty quickly
And also, WE LOST. Sure, nowadays most Brits acknowledge that the Empire wasn't really a good thing, but still, no one likes to admit that we lost, and so other more "glorious" moments in our history are taught.
I'm pretty sure other countries do exactly the same thing.