Pitch Inflation is a Bitch
During historical periods when instrumental music rose in prominence (relative to the voice), there was a continuous tendency for pitch levels to rise. This “pitch inflation” seemed largely due to instrumentalists competing with each other, each attempting to produce a brighter, more “brilliant”, sound than that of their rivals. This tendency was also prevalent with wind instrument manufacturers, who crafted their instruments to generally play at a higher pitch than those made by the same craftsmen years earlier.
It should be noted too that pitch inflation is a problem only where musical compositions are fixed by notation. The combination of numerous wind instruments and notated music has therefore restricted pitch inflation almost entirely to the Western tradition.
— History of pitch standards in Western music on Wikipedia
