When a person exposes themselves to non consenting witnesses be it on cam or anywhere, their motivations often depend on the specific circumstances of the incident, whether it’s a stranger on the subway or the female. Someone who is doing that shit acts within a context of specific power over people, that has a different flavour than, say, someone who does that on the subway system or out on the street. It’s a different power dynamic. Any sort of exhibitionist behaviour falls in the same spectrum of a delusional entitlement to do whatever you want, no matter what everyone else thinks and then some level of embarrassing or shaming the person that you’re doing it in front of or for. Many exhibitionists are driven by the thrill of exposing themselves alone, along with the reaction they receive from witnesses as they’re caught off-guard.
It is most likely that the behaviour of some people represents an aspect of misperception of how the technology world operates. Men could admire the idea of receiving or viewing such pictures from strangers, or on the web and they assume they can do same. Men notoriously misperceive women's sexual interest in them and project their own sexual interests and desires onto women. In this situation, men really are hoping and thinking that you'll be turned on and send them a picture in response.
As silly as this issue might seem to be, it offers some genuine opportunity for insight into the ways that modern technology reveals interesting aspects of sexuality and gender. It is probable that at least some of these men receive a sexual thrill at the idea of free gay sex chat with unknown women seeing their genitalia. It may be an aspect of exhibitionism, and some of these men probably masturbate as a part of the act.