This is one thing I disliked about celebrities that come out as bi and then later admit they are gay. It continues with the perceived notion that some people have that 'bisexuality' doesn't exist.
Saying your 'bi' is just a way to ease your fan bases shock/discomfort at the sudden change in your percieved sexuality. Its all about the molah.
Then, some time down the line. When the fan base has adjusted to the 'bi' tag and your not so successful - and also possibly your older enough to feel secure in your skin, you quietly drop the 'bi' and ease in the 'gay' tag.