Preventing children AND STDs is a very powerful motivator, usually for both parties involved.

It's simple really. Teenagers tend to take more risks. A possible pregnancy is a good reason to use a condom, as a side effect a lot of stds are also prevented. Removing the pregnancy possibility from the equation removes the need for condom use.

Yes, I know when I was a teenager, getting a girl pregnant seemed like a FAR worse outcome than getting AIDs and dying. I'm not sure if you think teenagers lack basic reasoning skills, or if this is actually your personal reasoning skills being projected onto all teenagers.