Why do so many people play these insane mental gymnastics instead of just saying "Yeah, I'm bisexual. So what?"

It's baffling.
Chasers who love cock and balls will argue for hours that they are 100% straight.
Women who lust over or fall in love with masculine fictional characters insist they are 100% lesbians.

Why is it a problem to say "Yeah, I guess I'm bisexual, although I prefer (gender) or feminine/masculine features over all.")