[T]he multilateral treaties, conventions and agreements of an economic or technical character enumerated below … shall alone be applied as between Germany and those of the Allied and Associated Powers party thereto:
. . . .
(22) Convention of November 16 and 19, 1885, regarding the establishment of a concert pitch.
The problem is pitch inflation.
Basically, tuning slightly higher than what the composer intended, will make the performance sound more brilliant.
What if it’s death march as the second piece and your want to tune lower, do you need to re tune your piano or do you carry your 2nd piano in your pocket?
Well, you don’t do that. You pick one frequency, in our case it was generally 442 Hz, and then you play the whole concert with that.
Re-tuning a piano can easily take an hour. And re-tuning an orchestra is just as well a multi-minute cacophonie. The audience would rather listen to a slightly too brilliant death march than that…