Male gymnasts have their legs covered and their arms bare.
Female gymnasts have their arms covered and their legs bare.
How come???
You might want to look at this thread. It answers some of your questions and, at the time of this post, is two threads below yours on the front page of this forum.
Weeeeellllll, speaking as yer boring vanilla hetero man, I'd MUCH rather gaze upon a man's well-defined fore-arms, and a woman's lithe and muscular legs, than the reverse.
I mean no disrespect, just a personal observation 
Cartooniverse
Turbo:
I was inspired to start this thread by reading the “well-dressed gymnast” thread (and didn’t want to hijack it).
Cartoon:
Yes, I agree. Except that I don’t even gaze upon the men, I’m only interested in the women. I sure do love how they look in those leotards.
Check that thread again. It has been hijacked in a big way.
Yes, and how. Though thanks to Lance here, my question did get answered.
That tank top has been standard male exercise garb for over 100 years (worn also by basketball players and boxers). I gather it evolved from the undershirt–in photos from the 19th century they certainly look more like undershirts than they do now.
Female leotards have also had sleeves for a long time, though ballet leotards usually have three-quarter-length sleeves. Don’t know why, though.
I love the look of the women’s leotard with long sleeves and bare legs. The arms covered full length makes them look sleek and elegant. Also, the arms being all covered emphasizes the bareness of the legs all the way up to the top of the hips. It’s such an unusual, but strikingly attractive, look and you never see it outside of gymnastics.
BTW, I have taken ballet class, and the long sleeved-leotards are as prevalent there as the three-quarter-length ones. I miss the 1970s when women wore long-sleeved leotards out everywhere. Maybe that fashion will revive someday.