Bisexuality involves a conflict. In this particular case, it is the conflict between heterosexuality and homosexuality. As anyone familiar with Aristotle's Poetics
knows, conflict is at the heart of all drama. Choosing to remain bisexual doesn't resolve the conflict: only a choice between homosexuality or heterosexuality leads to a satisfactory resolution and dramatic denouement.
Happy, contented bisexuals can't be at the center of a drama, because they lack the requisite internal conflict (see, e.g
., Chasing Amy
). At best, they can be peripheral figures.