The lighter side
- After the American Revolution, the British we're not at all happy with the colonists and had had enough. The very first thing they did was repossess the u in colour, leaving Americans with the much less colorful spelling of color. They took back most of the e's that like to hang around the back end of a lot of English words and King George insisted that all access to the word bloody used as an adverb be denied the upstart Americans. The colonists were actually fine with this as they had long favored goddamned over bloody anyways. There was a bit of a sting felt to the loss of cheeky, and it remains a mystery to this day why in replacing the words Water Closet, and the loo the Americans chose Bathroom and toilet.
- For the same reason we are required to "press one for English". Makes one wonder, doesn't it?
So in conclusion aside from all that literal and historic imformation... It is basically because the history between England and America was so tense and annoying that they kinda and secretly despised each other so they found as many possibilities to make them different to each other. Of course because people have different opinions and are from different places there are different answers but secretly I think we all know its just because of pure rivalry :)