RockNRollApartment wrote:
I don't know anyone who ever thought "no, I cannot have sex with this person, oh wait I can get the MAP, so I guess I will!"
This.  Also given how PlanB you need to go into the pharmacy for as opposed to condoms which you can grab off the shelf at any store plus through in the cost differential.  Convenience and cost is key.

And fun fact, I was more responsible when it came to making a dude wear a condom in HS then I was in college or have been since (and I was on the pill through all of it).  Obviously not everyone is but that includes "adults"