This may be over-exaggerated. If a native British English speaker were to start using Americanisms like "stroller" or "diaper" in the UK, the reaction would be biting. Indeed, one often hears laments about how English is now becoming progressively "Americanized". I have even come across certain ignoramuses in Ireland who decry "gotten" as an Americanism, when of course it's not, it having been used in Irish English since the language was first brought to the country.In many cultures, among them the English speaking area, people reject the idea that any kind of government agency, however democratically legitimated, should have the power to regulate language.
This is very closely related to the concept of freedom of speech which includes the right to use language in a deviant way.
I see no problem with having a regulatory body for English (we accept them for Irish, Welsh and Scots Gaelic after all), though for most people, the OED already fills that role. I actually think it might be quite a good idea as the standard of English as spoken by the average citizen in large parts of both Britain and Ireland remains quite poor.