The answer about factors is very simple - Japanese porn is always produced in accordance with
Japanese Legislation.
You should know that - Japan recently
raised the age of consent from 13 to 16.
The amendment to the Penal Code was passed by the Japanese Parliament ( Diet ) on June 16, 2023,
and came into effect on July 1, 2023.
This amendment caused some changes in Japanese porn production too - no more loli videos,
no more shota videos are produced.
Young people 16+ are already high school students (at least) - for loli fans this means -
they could only search for older, earlier videos/movies.