Why? Sense of humour?
How? The domain name was directing to an empty public folder (apache.1.3.27 at futuresite.register.com) from on or before 2003, was up for sale with Go Daddy on or before April 2009, and sold to the NSA on or before January 2010.
[Edit: Apologies, did not see the above responses. So, bought by an individual rather than the agency. I see. Makes me wonder why Go Daddy were trying to resell it in 2009, perhaps he let his registration lapse a wee while).