Once, a long time ago, I was sitting outside the kindergarten with a mum and talking to her. She told me that her then four-year-old son wanted to know how children come into the world and she told him. He replied: "Can I watch the two of you make another child?"

I laughed heartily, but it also had another effect: I thought that modern children rarely have the opportunity to witness the union of man and woman and that they learn everything to do with sex in theory first.
Since parents and children usually sleep in separate rooms, unlike in the days when families shared a single room and children inevitably witnessed their parents' activities (and were not traumatised by it, why, because it was normal), this part of human sexuality remains hidden from them.

Even when people were predominantly Christians and perceived themselves as such, sex was not necessarily something objectionable, I think. But even if it did involve a certain threshold of shame for people, bearing children at home, for example, was also nothing unusual and so the children already in the family were able to witness birth as one aspect of sex.
It was only when we began to take births out of the home environment that not only the parental act of union but now also the maternal act of birth became inaccessible to children. Now, the third aspect would be courtship and specific rituals and traditions.

For example, I don't believe that western religion can be primarily linked to prudery, although that has become very entrenched in thinking, but that technology and prosperity can largely be seen as the cause of people making their biological and natural sexual urges and adult practices inaccessible to children - unintentionally, in fact.

Modern people tend to make the mistake of looking at the past from the present perspective and merely recognising ideological or religious beliefs and convictions for sexual shame or inhibition. They rarely see what is going on right under their noses.

My assumption is that first there was technological progress and this began to bring about a certain closed-mindedness with regard to sexual permissiveness.

The separation of work and life is another important indicator. If children can't see adults in their courtship rituals, they know little about courtship themselves. How are modern people supposed to learn about how a man wins a woman and vice versa if they never witness such natural processes? Engagements, weddings, traditions where the age of a man or a woman plays a role, are all in decline and lost meaning.

Since people want to witness other peoples sex activities and rituals, they shifted this need to the world of the screen. Since the screen is only second hand, it poorly serves what the individual might long for. Porn and prostitution is a phenomena and from what I think, an expression of what can go wrong when humans suppress their biology.
When children reach puberty, they have no idea what masculinity and femininity actually mean. As a result, both they and their parents begin to fear this time, because the naturalness and simplicity of learning by watching their own relatives is no longer guaranteed.

So, yeah, I agree very much with what you said above and tried to give my explanation to that. I hope you don't mind the long comment.