While looking thru YouTube for pop music, I realized something. Today's 'Cute' Japan didn't exist in the 70s or 80s. This Hello Kitty World Japan has only been around for the last two decades. Furthermore, I believe the social look is related to the mangas of the time. Whether manga is setting the trends or merely reflecting the existing trends of the time I do not know, but there is a strong correlation between the two and a dramatic change in the look of the girls since the 70s.
The 70s
The manga was very cartoonist with little effort to depict the human anatomy correctly. Often the characters had three fingers and a thumb. There is no over all sense of cuteness in the manga and the Idols of the time also reflect this. Idols of the 70s often debut at 15~18 yet none looked 15. People tried to look in their low 20s.
Manga 70s
Idols 70s