It's simply that (some) English don't put their brains into gear before talking of nationality. I find myself using British and English interchangeably sometimes and have to make a conscious effort not to. It's also simply the fact that Scots are generally more aware on a nationalistic level (and rightfully bristle against being sidelined by England) but, well... uh, English people don't feel threatened in this way.

It's harsh but I think that's why.