Luckily this is MN so I expect someone who has a PhD in upper body osteoefficiency in garment divestment will be along in a moment to explain.
Ooh ooh! Me, me!
Okay, not true, but at a guess I’d say it’s to do with breasts and differences in construction of female and male shirts.
With buttoned shirts a woman would typically unbutton completely then remove, as female shirts (blouses) are often fitted. Men’s, not fitted so cuffs and collar unbuttoned, off comes the shirt.
Even with t-shirts a woman will be more likely to remove clothing in a way that exposes front first or front and back simultaneously so as not to have the shirt hitch under the breasts. Men have so concerns so can swiftly remove from back first.
Just a theory.
Also, Portlandia is now on my Watch List.