Their point is to achieve a goal by the use of intimidation, to provoke reactions from the authorities by their actions. What demographic is going to be more likely to provoke a response when targeted, than teen girls? The only ones that occur offhand are children too young to congregate in large numbers. The beauty of this is that they have religious issues with it as well. If they were to target a school or some other facility, they could hit some of their own. No one they see as a good person or decent young woman would attend the concert of a little slut who prances around provocatively in such scanty clothing (actually, I don't know anything about the singer in question beyond her appearance in a phone service commercial, but it's probably a good bet these days), and can point that out when questioned about the subject of their attacks. They probably had something similar in mind with the Orlando incident but underestimated the degree to which political correctness has infested the national discussion in the US, as well as the suicidal extent to which the governing, academic, entertainment and media classes are willing to turn a blind eye to the intentions and actions of the Islamic terrorists themselves, and didn't anticipate the rush to declare the attack an act of discrimination.