I think a lot is to do with the Catholic church and it's hold on people's personal lives as well as the church's influence on government policy.
There was no real sex education in school, and I'm not sure if it is even covered well now.
Also, complete upbringing for most people was that sex outside marriage is forbidden, and simply not talked about.
These things take time to change. But on the positive side, it means for the most part, we have low expectations!!