It may be their culture
Mostly religious reasons in India...and culteral reasons in America.
They follow strict moral code that does not allow them to dress so conservatively. Things such as esposing face and other body parts would display an openness to the flesh. Also ths comes down from generations of women as well. Also, it would warrant unnnecessary attention, which is why mosy Indian women if they do bear midriffs, would wear a sari to cover up.
Cultural differences. Why do women go topless on French beaches, but get arrested for it on most American beaches?
Even a swimsuit is a big thing for an Indian girl. It is modesty. Is considered indecent to show a body in public. Only a few city bred girls wear a swim suit.
And Indian village girls bathe in rivers and ponds fully clothed! They are good natural swimmers and swim fully clothes which is wearing long skirts.
CULTURAL DIFFERENCES. In France for example, women can go topless on the public beaches,a thing which would promptly get them arrested for indecent exposure in the United States and most other places. Every culture has its no-nos,and Indian culture is simply alot more conservative than that of the US in very many respects. In Nigeria, the Indian sari would be considered risque amongst most conservative folks as it bares the midriff. The respectable Nigerian lady wants to look trendy but COVERED. A respectable American mother can wear shorts in public without raising any eyebrows but a respectable Nigerian mother until very recently indeed ,would only wear shorts at home,and even now, would probably not attempt a pair of shorts that exposed any thing above the knee, so as not to scandalise her inlaws at least. Muslim women are prohibited from wearing noisy shoes from what I'm made to understand. And in Elizabethan England, a maiden lady would be expected to bare her bosom nearly to the nipples as a sign of her virginity but keep her arms covered to the wrists or be written off as a wanton! It's all about the cultural environment.
Indian girls are more conservative than Americans, so they like to cover more of their body.
because Indian girls have ugly mid sections