Because in modern society, some sensible people believe in individual freedom and making personal choices, without external fear or pressure.
I have no clue, but that does not matter. What matters is we are accepting of all sexual orientations.
that is because people think that being bisexual is actually cool
It sure is being seen a lot more. Just a phase I suppose
It's not becoming a lifestyle choice. People who make out with the same gender while being straight are not Bisexuals. Bisexuals genuinely like both males and females. Those who do not like both are either bi-curious or they're seeking attention.