Because there are more homosexuals, bi-sexuals, and metrosexuals than previously estimated.
No, it is because the CDC is gearing up for the next big AIDS extravaganza and needs some alarmist news to make a headline and remind congressmen to vote them more funds. The tipoff is the false attribution of 16% to heterosexual activity. What they mean is 16% among heterosexual IV drug abusers.
Work hard all of your life, pay the bills and rent, send the kids too college.
But, suck one big one, just once, and you're gay forever!