I've read that today's standard British-English spellings didn't becme standard until AFTER the colonization of North America, and that in regard to many of the words spelled differently on either side of the "pond," the US version accurately duplicates the 15th/16th century English usage that was brought across the sea, while today's UK spelling is of more recent vintage.

In any event, in answer to the question "why doesn't someone enforce a standardized spelling," there is no authority in any English-speaking country able to (or even trying to) rule upon spelling and grammer, etc., and of course it's hard to imagine any way of enforcing any such effort.

There's some kind of quasi-governmental apparatus in France whereby the Academie Francoise protects the sacrosanct rules of the French language. I can't imagine what they can actually do, short of burning books...