It’s all in the way that girl/boys shirts are made.
Girls shirts have less armpit room then boy’s do and are generally shorter so pulling it off over your head is more practical because by lifting your arms all the way up you make enough room for the sleeves to just slip off.
Boys shirts have more room and are generally longer so it is easy to slip them off over your head.
but if you take a girls shirt off like a boys shirt you will get your arms caught because there isn’t much armpit space.
and if you take a boys shirt off like a girls shit you will still have your head in it when you’ve lifted your arms all the way up because of the shirt’s length.
It has nothing to do with us. It is entirely to do with how our shirts are made. I figured it out for you. YOU’RE WELCOME!