Why 432hz Tuning?

There is no world standard for tuning. In the U.S, , 440hz A is the accepted standard. I recall buying a tuning fork for my guitar when I first started playing and it was a 440cps A (that's what it was called then). In Europe and in the "Way back" it was pot luck.

Even today, I have albums from the 60's and 70's that If I try to play along with, I have to retune in order to match.  In the old days, string instruments had to tune to the house piano for recording sessions and it may or may not have been in proper tune.

Just as an addition, I have a friend who is blessed/cursed with perfect pitch. There are two types, relative and absolute. People with an absolute perfect pitch are very much disturbed when music is not aligned with their inbuilt standard.