Why the preference for sons has decreased compared to the past

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In the past, since there was no mass media, people only knew about Asian men.
But once people became aware of the existence of White and Black men, who are much better than Asian men, comparisons were made, leading to a devaluation.
The period when Asian men were young was particularly bad.
The decisive factor is that most fathers have children when they are older, and by the time the children grow up, the fathers are elderly, which leads to a tendency to marry much later.
Regarding groups of elementary and middle school boys, it's just a matter of degree; I doubt many people actually think they are "good."
There is still quite a preference for men in some areas, and among them, most private companies still seem to prefer men.