I grew up in Florida and I never heard of this until I moved to the Pacific NW.
High Schools in Washington and Oregon still have these dances.
My wife is from there and was surprised when I asked her what the deal was.
She knew the name of the character right away.
So she knew about the concept and not the reason for the name,
and I knew the opposite.
I was terribly geeky in high school,
but I found that years later, a pal of mine from school went to our 10 year reunion
(I never would have gone anyway, but I was off on Army training at the time)
and he found out a few of the girls we went to school with,
told him they had a thing for me, but never said anything back then.
Geeky, yes, but still well-known as I was the cartoonist for the school paper,
and won all kinds of art awards back then.
To this day, I wonder what might have happened,
had they had Sadie Hawkins Day where I lived.
But I know no matter what alternate reality,
I couldn't be better off than where I am with my wife today!