Beards have been tabu for most soldiers since a general noticed a few thousand yeas ago that lots of warriors died when the opponent grabbed the beard and pulled the head down while swinging a sword.
The American experience with beards was really fostered by the 2nd Great Awakening where everyone grew beards and was whipsawed by WWI and the need to wear gas masks. This WWI and WWII idea of the rugged American being well shaved then got supported by the long haired freako hippies in the 60’s.
Going back to beards was actually an incredible sea change for American men, probably brought on by the “real” men fighting in AFG with mega beards. (And yes, I have pictures of mine)