Some "women's specific" bikes have different proportions (fractionally) because women are supposed to be proportioned differently than men.

This is an interesting take on the topic (Are Women's Body Proportions Different From Men's? -) What is says it that proportionally women tend to have longer torsos and shorter legs, but are also more comfortable riding a little more upright because their centers of mass are further forward when they lean forward, putting more stress on the shoulder, arms, and hands.

So, the shorter top tube makes for a more upright riding posture, which most women (supposedly) find more comfortable.

Some women's bikes have shorter top tubes compared to seat tubes, for a given frame size. if you have a short torso and long legs, a "woman's" bike might fit you without needing to resort to a a very short stem which you might need on a "men's" bike. Or not.

As a group almost everybody is "average" and individually almost no one is "average."

Best thing to do is either sit on the bike and get real good at reading geometry charts.