Bicycles in the earlier days were not made of materials as strong as today. The horizontal crossbar on the bike frame was included to add strength to the frame. The high-quality bike frames today are mostly made with carbon fibers, giving the bicycle much strength.
The bikes made today have frames strong enough that they usually do not require the addition of crossbars. The bike frames that still have horizontal crossbars are men’s bicycles. It may sound counter-intuitive as the absence of the bar will reduce the chances of racking the guy in case he slips off.
The bar poses a different kind of problem to women that mostly wore dresses. Mounting a bike requires lifting the leg over the crossbar, and if you are wearing a dress, that is bound to expose almost the entire leg which was considered quite scandalous back in the day. The bike makers started making bike models with slanted the crossbar down to make the bike mounting more ‘dignified’ for women. Such designs were particularly for women, but they ended up weakening the bike frames. But why would a fine lady need to use the bike roughly anyway? Only the men needed to do that.
Women do not necessarily have to wear dresses or skirts all the time anymore. Bless the time when the tradition ended! However, the tradition of making bikes without crossbars has continued. The bike frames today are made with such strong materials that the absence of crossbars does not put a significant impact on the strength of the frame, even if you ride it on a rough terrain. In fact, some BMX bikes for men today are made with slanted crossbars to minimize the chance of injury while performing tricks.
The bike designs today do cater for different needs of men and women differently, but this does not include the ‘sophistication’ problems. The high-end bike frames made with carbon fibers do not require crossbars, but the bike makers keep in mind the physical difference between men and women. The designs account for shorter torsos and arms of most women, modified hip placement, and even modified seat designs.