I think a lot of you guys are missing the point of the original situation… parents at the time didn’t want their kids having premarital sex. And the closer you are to a person, the more likely it is that you guys are going to have sex.
So, keeping their relationships as shallow as possible was thought to help to limit how much premarital sex your kids had.
“Going steady” meant having sex. If you’re not “going steady” with anyone, then you’re not having sex. - Was the thought at the time.