Calling them "girls' bikes" or "ladies' bikes" may be slightly sexist or may be a reflection on history wen females wore cumbersome dresses and males did enough exercise that they were fit... until they died fairly young. However, I think there is a valuable role for these frames, especially for older or less flexible people who, regarding of dress, have problems going over the tube. BTW, the "mixte" design is a bit more rigid, but my mother will tell you that her 1975 Peugeot mixte is much harder to straddle than her 1935-1940 girl's bike ever was.

People who have problems going over the top tube of even compact design bikes are not doing long distances nor they are carrying heavy loads, except sometimes in a trailer. A bike with fully loaded panniers is much too hard to control when one has problems straddling a bike! And for purists who cringe at the idea of a step-through frame anyway, I would respond that the single-tube design of many folding bikes is even more ludicrous from a structural point of view. But just as folding bikes need to be heavier, beefier (or flimsier) than an upright, so do bikes with step-through frames. And in both cases, the design has advantages (ease of going on/off) and drawbacks (added weight or loss of rigidity).