Why 432hz Tuning?

The St Louis Symphony has tuned to 442 for many years. 
 

FWIW, ChatGPT reports that the move for standardized tuning gained ground in the 20th century. From the 1600s into the 1800s tunings varied widely according to region and different musicians. The AI says a standard tuning for Bach and his contemporaries was 415, Beethoven from 430 to 450. 
 

Given the time it took to travel and communicate, and the lack of recordings, it makes sense that there could be wide variations in “standard” pitch by region. The AI does say that it can give incorrect results, but I’d say there’s evidence for a mostly lower standard, but not just 432. 
 

it would be interesting to hear some music played at lower tuning standards. Know of any?  Does John Gardiner tune lower?  

@edcyn , I understand what you are saying. While this is really a separate issue, it further makes my point. It may not be practical, or may be impossible, to tune the fiddle to achieve the “magical” A432 tuning. In a way, it’s the same problem for winds. One can pull the mouthpiece out on the neck of a saxophone, or the lead pipe on a trumpet, in order essentially extend the length of the instrument and hence lower the pitch, but it is impractical since the instrument is not designed that way acoustically. Doing so will throw everything off and the instrument will not be in tune with itself. IOW, the pitch relationship between notes will be altered. One might be able to achieve A432 with one note, but the fifths and octaves (just two examples) will be way off with no practical relationship to A432.

Interesting reading. It should be noted that while it is true that tuning lower than A440 has been used through musical history, there is no indication that actual A432 was used; and certainly not as a “standard”.

https://www.mozartpiano.com/articles/pitch.php

@zgas-music, in answer to your question, note the reference to Gardiner’s recording in the “End Notes” of the article above.

A point of clarification:

The eagle-eyed who read the article that I posted above will notice that there is a reference in it about the way that the pitch of a tuning fork lowers as its temperature rises.  This may seem to contradict what I wrote about the way that pitch rises as instruments in an orchestra warm up.  Not a contradiction at all.  The reason that instruments go sharper as they warm up is that air becomes less dense as it warms up.  Being less dense causes the air inside the instrument to travel faster, so the pitch rises.