Years ago, after visiting a fascinating Shunga exhibition at the British Museum, I researched this topic (purely out of interest in art, of course):
For over a thousand years, Shunga https://en.wikipedia.org/wiki/Shunga woodblock prints depicted everything we admire today on beautiful websites like this one.
Scenes of fellatio, though known and practiced in ancient Japan, were rarely depicted. The reason for this isn't immediately obvious, but it's easy to explain: Shunga favored large male genitalia, while women with very small mouths were considered feminine beauties.
Or, put simply: If the penis is bigger than the woman's head, it just doesn't work.
