How about it's movement limitations were promoted to that of a queen -- we just replace it's representation as a queen so we don't get confused, in reality it's still that pawn, but it moves like a queen now.
Also she has a few (equally attractive) twin sisters who fancy wearing dresses while mercilessly hunting down slow moving old monarchs.
Think about it. How can a pawn be promoted to a Queen? It would make more sense if we were to say that the Pawn infiltrated the enemy's castle, rescued the Queen, and traded places with the Queen. But what if there is already another Queen on the board? Is the rescued Queen a Queen from another Kingdom?
Wat?