I think you'll find you have the French to blame for that. After the Norman Conquest of England in the 11th century, they standardised (standardized) the language after Old French, which uses 'our', not 'or'. The 'or' was from Latin, after the Romans conquered England earlier. So technically, Americans are influenced by Latin (a dead language) and not the latter French. Weird, right?
Besides, Americans are as confusing. Using 'Z' (pronouncing it as "zee" (US) for some reason and not "zed" (UK)) in some cases but not others for the same sound.
If phonetically, 'Standardise' (UK English) is changed to 'Standardize' (US), then 'Reason' should be spelt 'reazon' and pronounced "reazee-en", right?
Shouldn't "standardize" be pronounced "Standardizeed" too?