Because that's the way it was listed in all my history books in high school and college. I know it was the CSS Virginia in Condederate service, but I have read maybe 20 books that listed it as the Merrimac. Naturally, these books are all older ... I graduated from high school in 1968 and you probably have never read the same books.
In the end, I recognize either name and don't really give a hoot which one it is called ... I recognize them both ... the events are the same either way, as are the dispositions of said ships. And I lived in Phoenix during the Falklands war and it was reported as the USS Phoenix there in the papers AND the news, though the name General Belgrano waws also stated at the end of the telecast. So I remember BOTH names equally well.
Again, this isn't related to flying, so let's drop it, OK?
If not, I decline to continue in here per forum protocol. The location of the Monitor is: Coordinates: 35°0′6″N 75°24′23″W. The CSS Virginia resides on the bottom of the James River.
I graduated in 1965. My daughter lives just a few miles from where the battle took place, and the CSS Virginia's resting place.