I was a teen in the 90's too and I used condoms all the time, plus the pill. Like Mintie, AIDS was still in the media a lot back then and it scared me more than pg.
As to why teens have sex outside of marriage? I won't say I've had a heap of partners, I got with my DH at 17. But I've had a quite a few, and I don't regret it a single bit. I had already done the rounds (that sounds bad lol) I had my fun, and when I got with my DH and fell deeply in love, it was for life. I'm now almost 34 and wouldn't change a single thing about my life before him.