When Great Britain, Canada and Australia all spell it labour, why do American writers spell it labor?

I am talking about the proper name of political parties. The Labour Party, or Labour for short is a proper noun. Today's article about Australia's apology: "Rudd made the apology the first item of parliamentary business for centre-left Labor, which won power in November last year, ending almost 12 years of conservative rule." It should read centre-left Labour. Then I notice that centre is spelt correctly and I wonder who exactly wrote this article? In Canada, Britain and Australia it is centre-left Labour and in USA it is center-left Labor.....totally messed up!

The point of my question really is why are they changing the spelling of proper names? This is not something to be translated or changed because you spell it differently in your own country. It is a name. Then the word centre through me because if it was an American author wouldn't they spell it centre???

Many American spellings differ from English spellings. The original settlers to New England taught English Webster's spelling-rules which omitted 'U' in words ending in 'OUR' (eg: honor/honour & color/colour, etc) and also promoted single consonants instead of double consonants in 2nd syllables, (eg: traveler/traveller, etc)

The influence of multi-cultural immigrants to the US, has also meant that American spellings have gradually evolved over the centuries, becoming more phonetic than British spellings.

American spellings are now becoming more universal as Microsoft software defaults to American spellings and often does not recognise British spellings. (On the other hand, our quaint British spellings are a product of history, influenced by Shakespeare, Chaucer, Claxton, et al).

Words ending in OUR have been changed to OR in America (labor/labour)

Words ending in IOUR have been changed to IOR in America (behavior/behaviour)

Many words ending in YSE or ISE have been changed to YZE or IZE in America (analyse, categorise, standardise) Exceptions: ARISE, DEVISE (This American spelling is also acceptable in the UK)

Many words ending in YSED or I SED have been changed to YZED or IZED in America (categorised, standardised) (This American spelling is also acceptable in the UK)

Many words ending in ISATION have been changed to IZATION in America (categorisation, standardisation) (This American spelling is also acceptable in the UK)

Words ending in RE have been changed to ER in America (centre, metre)

Words containing the silent letters OUGH have been changed to in America so they are spelt phonetically (doughnut, hiccough)

Words containing a double consonant before ING and ED have been changed to one consonant (travelling) (This American spelling is becoming acceptable in the UK)

Words which vary in spelling according to whether they are nouns or verbs have been standardised in some cases. eg: verbs: practise, license (NOTE: the word standardised follows the ISED rule above)

Because during the early 19th century Noah Webster invented American spellings to distinguish American English from British English. America was a country coming in its own right, and he felt words should do the same, so he invented American spellings, like taking the "u" out of words like labour, colour, honour, so they became labor, color, honor, also, center, meter, etc.

It isn't totally messed up, far from it - US English has a few small differences in its spelling system. There are only a few:

ize/ise
Socialize (US)
Socialise (UK)

er/re
Theater (US)
Theatre (UK)

or/our
Color (US)
Colour (UK)

You can't expect a worldwide language to stay 100% consistent. The amazing thing is not how different the varieties have become but how close they have stayed.