system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why do boy bikes typically have a bar across the top whereas girl bikes do not?

And that carries over from kids' bikes to bikes for adults.  Just seems to me that, if anything, given human anatomy it would be reversed.

Edit to add:  Thank you all for pointing out that women/girls traditionally wore skirts in which that bar would present a problem.  So, I guess two better questions would be:

1.  Why is it still common?

2.  Why do male bikes have that bar at all?
gpt
Women used to wear long dresses to used to have to have to "step through" the frame in order to preserve their modesty. Males on the other hand could just pop their leg over the top. The tradition has just been maintained on most commercial bikes.