If it were about morality, sons' dating behavior wouldn't be tolerated with a wink and a smile. If it were about pregnancy, parents would discuss contraception with their daughters instead of keeping an embarrassed silence. If it were about physical safety, parents would teach daughters self-defense and personal caution just like they teach defensive driving, instead of banning dating and social outings outright. When stripped down to its barest, most subconscious form, it's all about power. Men want to dominate women, and what makes men most insecure is not being able to control female sexuality.
Parents are well aware that female virginity commands a premium in the marriage market.
Indian culture goes further than sexuality when it defines what it means to be a good Indian woman. The traditional roles say that women should be smart, but not smarter than men. Many of my intelligent women friends feel they have to play down their intelligence to attract men. Several of them are having their arms twisted to marry right out of college. These are bright, articulate young women who would rather go to grad school.