Why there is so many Japanese star?

I am not sure if this is a problem with 'so many AV actresses are Japanese', although there are many women in Japan who are entering graphy - for example, Azusa is estimated to have 10,000 people each year.

There is nothing to do with the government

But this has nothing to do with the government; in fact, Japan's censorship laws are very strict, and all materials must obscure or otherwise cover the genital area. Of course, the government has not taken the initiative to “export” graphy or encourage women to enter these industries, but from a cultural perspective, Japan is interesting because, as you said, the respect that stars give in other cultures may not be common.

there is a strict dividing line between the industry and “family”

First, in many countries, there is a strict dividing line between the industry and “family” or “mainstream” entertainment. It is rare to see people crossing these borders - Sasha Gray may be a rare example of Hollywood. However, in Japan, the border is relatively smooth. Azusa also said in the interview that some women's dream of entering the industry is to make her famous; to become a mainstream actress or celebrity. In addition, this may not be considered "graphy", but many mainstream Japanese actresses and models, such as Toda Hikaru or Sasaki Hime, started their career 'gravure model'.

Japanese game shows on mainstream TV channels often seem to have less reservations for AV actresses. This is not a taboo for their profession, but just whether they have a high enough popularity to appear in the variety show.

Unlike sex doll in Japan , it is not a secret that womans' idol members (such as AKB48) sometimes enter the adult industry after they “graduate” from the group. This is by no means a universal phenomenon - for example, although there are many womans and idols in K-pop, it is unthinkable for mainstream celebrities to "drop" to actors in Korea. It's like Taylor Swift announced that she is singing and entering the adult industry. It may be difficult to calculate for the rest of us, but it is not uncommon in Japan.