It comes from the same reason we say guar gum.
I don't know for sure, this is only my opinion, it comes down to simple accents/dialects. Americans speak American English. British speak British English.
Americans say cars have trunks. British say cars have boots. I also think since the British make the car they are saying it right.
But you have to admit it sounds funny when an American says it that way.
Sorry, I don't have an authoritative answer to your question. However I can speculate. The big cat, jaguar, is native to the Americas.
If I remember correctly, it's range extends from the Sonoran Desert that straddles Southern Arizona and North-central Mexico, down into the South American countries. Because it's closer to home and discussed more frequently than in Britain, we prefer a pronunciation that has fewer syllables. As an American, I do appreciate a few things about British English.
One example is a common metal. We Americans spell it as aluminum. For some reason, that's difficult for me to pronounce.
On the other hand, the very British aluminium just rolls off the tongue.
Because we are americans and we are english. -smile.
War is a hobby for Americans dear friend without a war the President cannot sleep.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.