The reason is that a military defeat of Britain will bring about the disintegration of the British Empire. This would not be of any benefit to Germany.
“Your living is determined not so much by what life brings to you as by the attitude you bring to life; not so much by what happens to you as by the way your mind looks at what happens.”
“I would not say that I was, these days, a 'student' of philosophy, although in my youth I was quite deeply involved with certain aspects of the British pragmatists.”