ujm, a good question. Maybe because the skirt case involves understandable pull by current society. If she is a BT or MO school grad, then this is the environment fault to begin with and we need to give credit for whatever she is doing right. If she is a lapsed charedi, then it is also fault of the environment that did not nurture her. On the other hand, while geneva is of course present in the society, but it is not considered “normal” and is even prosecuted. So, the person got to have a strong internal drive to follow it.
Also, the ganav pretends to be a “frum” person, while the short-skirted one is obviously not hiding much. Isn’t it why hazer is considered most reprehensible despite having 50% of simanim – pretending to be kosher?
That is as far as my self-psycho-analysis takes me. Any other explanations? Now, please someone explain the other side.