Many have pointed out that the different shapes have an historical origin in how women dressed at the time.

This also agrees with what I was thaught as a children: that the "low bar" shape was invented to allow women with long dresses and skirts to ride a bike more easily and to mount it without "being indecent".

However no one has provided any links to these explanations, yet. I'll fill the gap by providing some useful links to the history of the bicycle that cover the OP question.

Why are Men’s and Women’s Bikes Shaped Differently?

Why Do Women’s Bikes Have Different Frames?

Pedaling the Path to Freedom

How the 19th-century bicycle craze empowered women and changed fashion

These article all confirm what I and other have said about the origin of the different shape, but also point out that this allowed a real costume revolution at the turn of 20th century, empowering women to become more independent.

ANSWER: the "low bar" shape was invented to allow women with long dresses and skirts to ride a bike more easily and to mount it without "being indecent". This also agrees with what I was taught as a child.

However no one has provided any links to these explanations, yet. I'll fill the gap by providing some useful links to the history of the bicycle that cover the OP question.

Evidence:

• Why are Men’s and Women’s Bikes Shaped Differently?

• Why Do Women’s Bikes Have Different Frames?

• Pedaling the Path to Freedom

• How the 19th-century bicycle craze empowered women and changed fashion

These article all confirm what I and other have said about the origin of the different shape, but also point out that this allowed a real costume revolution at the turn of 20th century, empowering women to become more independent.