Porn companies know this as well, which is why "Bi-sexual" content has never been released on a wide scale because there has never been real demand for it.
Back in the days when porn companies were in the gray zone between making art for groovy progressive types and making money from the most people they could, flicks like Live-Bi-Me, featuring scenarios containing men, women, and men AND women, would show up occasionally.
Today companies work according to a proven formula, dictating that there needs to be a certain number of sex scenes per picture and a certain number of positions within each sex scene. If that seems cold and calculated to you, maybe you should move to Iran, you freedom-hater.
It is always fun watching the "classic" porn movies (Live-Bi-Me was made in 1990. According to the press release, it was "an attempt not made very often at the time, and it works very well." The only thing that makes me doubt that is the conspicuous lack of Live-Bi-Me #57 anywhere, or even Live-Bi-Me #2) and the cast of characters look like a gay Hair Club convention getting the last drink order in.
As a cultural snapshot, remember that 1990 was also the year The Godfather III came out.