Some people may have been bicurious, or simply curious about their sexuality, but people who are bicurious may not truly be bisexual and later realise that their orientation is something different. Saying that everyone is bisexual, to me, is like saying that everyone is of one ethnicity or race. Tell me, is everyone heterosexual? How about homosexual? What about the various other sexualities that exist? Bisexuality is the attraction to two genders and not everyone is attracted to two genders. Some people may only be attracted to one gender, or they may be attracted to more genders. Therefore, while bisexual people are real, not everyone is bisexual.
I am not bisexual, so that means that everyone is not bisexual. Why would everyone be bisexual? I would like to know what you were thinking when you came up with this question. Not to ridicule you, but it would be interesting to know. Do you know many bisexual people?