"While male gymnasts either wear loosefitting shorts or full-length pants... women and girls at many levels of gymnastics have for decades tended to wear leotards cut high up their thighs."

"Unitards, however, are allowed, as are leggings of the same color as a given leotard. In addition to helping some competitors feel more comfortable, such outfits can be favored by athletes for reasons of cultural and religious modesty. 'We women all want to feel good in our skin,' [a German gymnast said]. 'In the sport of gymnastics it gets harder and harder as you grow out of your child’s body. As a little girl I didn’t see the tight gym outfits as such a big deal. But when puberty began, when my period came, I began feeling increasingly uncomfortable.'... 'So now where we’re seeing athletes speaking out about uniforms, you know, it really could be symbolic of the need for athletes to have more voice in general in the sport context,” [said Elizabeth Daniels, a University of Colorado psychology professor who has written about the sexualization of female athletes], 'which could alleviate some of these really tragic abuse cases that have come to national and international attention more recently.'"

From "Wearing unitards, German gymnasts promote comfort, take stand against sexualization" (WaPo).

I'd rather see the female gymnasts in full length leotards because it would highlight the overall positions of the body — all the body parts in their changing relationship with each other — which is what we're supposedly judging in this sport. 

And the leotards really do seem ridiculously outdated with their spangles and other showgirl touches. It doesn't say: sport. It says: Little girls' beauty pageant. 

And these are little girls. I know Simone Biles is now 24 and reportedly even better than ever, and that's fantastic. But for the most part, we are looking at young girls. That makes it especially important not to wear costumes that only narrowly cover the crotch and that leave an expanse of buttock bare.