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.
It was hard enough to drive those heavy old cars back then under normal circumstances, but with a crazed monkey clawing you at the same time, it becomes nearly impossible!
But nevertheless, it's music ultimately that matters in opera, and opera is a piece of music reaching out as a vision in sound reaching out to the world.