I think because females have big possibility to be bisex ? I've read a lot scientific studies that say bisex females are 2nd majority after the hetero, and pure lesbian the minority
so its common to see some girls that we think are lesbian, can sexually aroused by males too
while in JAV those girls are pure hetero, and they still can't hide it
its more easy to do something sexual with your own gender if you are bisex, but if you are pure straight its very difficult
Well I think we (on an English forum) carries a Judo-Christian-centric baggage when trying to understand hetero- and homo-porn in both US and Japan. We think of sexual orientation similar to say between vegetarian and meat-eaters and omnivores... Yes some people are life-time committed vegetarian, some are doing as a phase or an experiment. Some only eats meat, some are just casual. We don't label everyone as a "type" or worry too much if he's a biological vegetarian or it's his choice of political expression. And if he's an actor, do we care too much he's eating a hamburger in a film role? But in the West, sex is an obsession and a taboo. The West get so hyped up about even same-sex kiss. There's so much hang up that sex is a sin and it's only tolerated between a Man and a Woman within a marriage and preferably for the pleasure-less purpose of making more devotees to a God.
I kinda stopped following Western porn around the time this "GG/BG/DP..." gradation was developing so I don't understand it (nor care) at all. But (1) it lets amateur girls to make some money doing gg scene without ruining her life (since the greater society sees it that way), (2) it's rooted in this anti-sex religion society.
For JAV, let me argue that historically most Asian (and Japanese in particular) men and women never figured out what his/her innate sexuality was. Love, marriage, children, these are just the natural way, no one ever told them "Search your feelings" (with echoing sound effects). Only a minority (mainly the rich and royalty) have the luxury to even think about his/her inner desires. Since they happens to also be making the rules, they don't make homosexuality such a repulsive crime against nature as early Christians did.
The point is most Asians do not obsess over the "self" as the West. We don't say, oh I am Gay, so I can't even look at a vagina or get a erection with a girl. Or, oh I am a pure hetero woman and can't let a woman lick my pussy. For us,
social norms,
duty etc are legitimate reason to ... maybe not totally suppress the
self, but to regulate, to moderate the
self. So for example, if a (mainstream) producer say, "You have the face of a raging lesbian punk rock", the girl won't say, "that's not me, I am straight!" The girl would at least listen to him and respect his opinion, and work with his view, perhaps obediently follow his demands (if he's a very successful agent). For Westerners it's a crime against humanity, for Orientals it's a fact of life. For JAV girls (and even guys) having sex with someone or even
something that's not your preference (say, sex with smelly homeless guys genre) is well undesirable but not unimaginable, especially... not un-
negotiable.
The only one left of my favs who hasn't done it yet is Rina Ishihara. Its really looking like almost all jav idols will do lesbian scenes now what a time to be alive!