USA is one Country where 50 states have their own Federal jurisdiction, UK is an ensemble of Countries which stand on their own accord, with their own history, customs, colours and pride. You can't compare there. Furthermore the colours of a Flag reflect that Country on the whole.
Samoa and Cook Islands have their own flags, rightly so I may add, why not those Countries that have a very proud past?
After all it is only a matter of one small graphics change.