Why do so many women in Hollywood thinks it's cool to pretend their bi?

I never see anyone with the same sex. They all are dating men or are married to one (I.E. Lady Gaga, Megan Fox, Fergie). The argument could be made that no one knows what goes on behind closed doors, but don't you think that you'd see some sort of behavior in public to show signs of bisexuality? Holding hands in a more than friendly way? Something so simple as a kiss on the lips? The cameras are everywhere for them and I never see this. I mean, if I were bi or gay or lesbian, I wouldn't want someone making it a "trendy" thing to say when I would have had to hide it for generations due to ridicule. South Park made fun of something like this with a "metrosexual" episode and Mr Garison (sp?) lol. But, I don't know what else to say other than it would be for shock value.