I taught our 4H kids to post and why, how it is better for the horse at times.
They were also showing in English classes.
Later, while working cattle, some parents that were cowboys, here and there, in private, one would ask me to show them how to post, which I did.
Most of them then went on to post while long trotting along, although I remember some that at times still just stood in the stirrups.
Some western horses have such a short, choppy trot that it is harder to post on them.
I used to tell them riding western or English or racing or any other discipline is like using different but similar languages to talk to horses.
They are close to the same, but there are some differences, like more or less contact and demanding more or less quickness or extensions of the horse, plus the technical riding each discipline requires.