It simply never occurred to these young women that sex before marriage was not required. It was a given in their minds, something they were entitled to do when they were “ready,” without regard for the children that might be conceived through their actions.
The media and schools have fixed in the mind of teens that dating means sex and prom means sex... as if that wasn’t bad enough GLEE even had a Valentines Day episode where a teacher castigated some girls for not putting out on V-day as “cold fish”. They are made to think there is something wrong with you if you don’t have sex as a teen.