Everybody involved knew - two seperate former belgian PM's have admitted as much publically on several occasions.
Instead of waiting until the economic requirements for a common currency were met, Kohl wanted to demonstrate that Germany, even after its reunification, remained profoundly European in its orientation. He even referred to the new currency as a "bit of a peace guarantee."
This is the clue really, political motivations over strictly economic ones.
High Admiral Snowy, Commander In Chief of the Naval Forces of The Phoenix Confederation.
Francis II, Holy Roman Emperor - The Napoleonic Wars Campaign.
Godfrey of Bouillon - Duke of Lower Lorraine - DVD.