Men naturally desire forbidden things much more than women, especially in tayvoh issues. They are more proactive and assertive in realizing their desires as well So when a boy goes off, it’s obviously not alright, but the pull in that direction is very strong, and he has the proclivity not only to want it but to actively pursue it.
It takes more for a girl to engage in these things; she has to break down many layers of tznius and bashfulness among men that she grew up with. For this reason it’s harder to break the image of the “bad girl” than the “bad boy”, not that the averah itself is any less severe for either person involved