Why there are so many teen pregnancies in usa where pill was invented about 50 yrs ago?

because "the pill" cost money, which you need a prescription for from a doctor (which costs money), and a large percent of families with pregnant teens can't afford health insurance as it is.
this question has less to do with "the pill" than it does for standard contraceptives like condoms and safe sex practices among teens.
it would be interesting to see the actual percentage of teen pregnancies now v/s 50 yrs ago, because some could very accurately argue that there are more teen pregnancies now simply because there are more teens now.