Why do people in the United States and Canada choose frame nail guns with different degrees?

As we know, in USA most peoples like using 21 degree framing nail gun, but in Canada people usually use 34 degree framing nailer,why do people Why do people in the United States and Canada choose frame nail guns with different degrees?

Anybody knows please talk the reasons to us!

We sold High quality Rongpeng frame nail gun 300,000pcs/year, also we know Australia

and North Europe people like purchase 34 degree Rongpeng framing nail gun, so why have this different?

this series framing nailers can save your lots money, and the parts  interchange with hitachi