Some say Rome fell when it was split into an eastern and a western empire ruled by separate emperors (hold on the history part is part of the funny). The eastern half became the Byzantine Empire, with its capital at Constantinople (modern Istanbul). The western half remained centered in Italy. But I think that they byzantine guy owed the Italian guy some money and couldn't figure out how to make change so decided to collapse the whole system and change the name of they city where he lived so that creditors could never find him. Why you ask would someone do something so world altering over something so trivial Roman numerals is the answer. You see Roman numerals are an interesting idea instead of numbers we will use letters then people have to figure out what those letters are even though they are secretly numbers. Does this remind anyone of math in high school (solve for X)? Many don't know the history of Roman numerals and the conspiracy to create them. They where invented by a group of rebels with the fall of the empire in mind. There objective was four fold and it collapsed an entire empire. Historians agree that the reason Rome fell because of a combination of such factors as Christianity, decadence, monetary trouble, and military problems. All linking back to Roman Numerals.
1.Christianity used the numerals to collect tithing "all you have to give is X% of your money" they would say and since no one could figure out what X was and didn't want to look stupid they did it and thus Christianity spread.
2.Decadence of course people where decadent they had no idea what anything was worth anymore a "golden scepter for only XCVIII that's a bargain!"
3.Monetary trouble since no one could figure out what the numbers meant at the end of the year everyone was having money trouble since they spent it all on number 2
4.Military Problems the military wasn't getting paid because the numerals where taking over and the Emperor couldn't find anyone who could explain it to him.
So as an act of desperation when the Emperor in Italy asked for more money the Byzantine emperor disavowed all knowledge of the dept hired a Jewish tax man and changed the name Constantinople to Istanbul. Problem solved but end of the empire. So now I can answer the song 'why they changed it I can't say' It was to keep the debtors away.