Why did Bradley Manning suddenly become Chelsea?

Why make a big fuss about announcing what everyone knew well before the trial started? Because Leavenworth is an all-male prison. This makes it look less like a courageous stance by a transgender individual, and more like a cynical ploy to avoid spending the next 7-35 years in Leavenworth.

(cynical quotes around certain words in the previous paragraph have been omitted to avoid discussing the general issue of gender as a fluid concept disconnected from biology)