As a bisexual human, I like almost anything when consuming the pornography. But I can never find good bi content. It's always some video that's 20 years old and so over produced and acted that it's awful to watch. But you can't find any decent modern content with bi themes. Or its a gay/lesbian video wearing a cheap mask.
Have you looked into alternative production companies? Erika Lust is my go-to for queer, feminist, equality-focused, fair porn. They have some stuff that's specifically catered to bisexuals, too.
Try it out
Similarly some independent creators will do it every so often. Usually you'll see some push back in the comments though because it's not their usual straight or bi-girl content
There's no good bi content, because film makers don't get bisexuality and don't produce videos for bisexual viewers (e.g. it's quite obvious that the main target of FMF videos is a cishet male audience)
Film makers just repeat the same stereotypes, like "threesome means hardcore sex", "all bi guys like anal sex", "only male pleasure matters", "all girls are bi (or at least will kiss each other to turn on their male partner)" and so forth
As a bi guy, I'd rather watch a nice porn with a pretty couple and fantasize about both of them
IMO, part of it is simply that most porn is 1-2 people. While there are ways to make a 2 person porno be bisexual-friendly (at least to me), it's not common. But you're right overall, the industry needs to step it up!
I thought most porn is bisexual because you always see the dudes balls and penis and cum. But then on I'm not BI, so I would not know what you're looking for.