well, that's why I said 'allegedly', Ethel. (I was born inside marriage, but only just, so I know it wasn't exactly universal.)
The actual thought processes will be more complicated than the ones I outlined, but the social bias was clearly against premarital sex, and many of those who grew up then still feel that system worked even if more honoured in the breach than in the observance. I welcomed the greater sexual freedom that became available from the 1960s, but even then it was clear it benefited men more than women.
There's more genuine gender equality in sexual behaviour now. Has it made people happier? Being over 30, I find it hard to say. Being under 30, young people probably aren't in a position to make comparisons either. I would guess that a more relaxed attitude to premarital sex has made for a more tolerant society, which I think is a good thing. But if I were a bit older I might reasonably feel the opposite, and take my place among the 30%.