Well, since I live there (here) I had better know the answer!!!! The reason is so as not to confuse this place, the capital city, with the state, Washington. Washington, D.C. and Washington the state are two very different places located in different regions of the United States. The state is located in the northwest corner of the USA, south of British Columbia, north of Oregon, west of Idaho, east of the Pacific Ocean! The capital city, however, is located in the east, in-between Maryland and Virginia. People who live in the District of Columbia refer to this place (which, by the way, is officially a "district" and neither a city nor a state, though it has some legal/governmental characteristics of both) as either just "D.C." or "The District". If I said "Washington" to someone else who lived here, they would reply, "You mean, the state?" I hope this helps! If not, ask and I will add more. :-)