There is an interesting history to the standardization of English, but I would also like to point out that on some level, standardization does not exist.
It is my understanding that English began to become standardized when the printing press was invented, since written materials then became more widely available and there needed to be some agreement on spelling, grammar, and definition. Prior to that time, there likely was some standardization in the Church and among well-educated people, but they were a distinct minority. Most people did not communicate with one another in writing, but in speech, so any lack of standardization could be clarified in person.
As the United States began to become more connected, with railroads, with the telegraph, with interstate highways, with the telephone and radio, and now with television and the Internet, English had to become more standardized so that people in all parts of the country could communicate with one another. The variability in regions or in various ethnic or racial populations interferes with communication that is among regions or different groups.
Now, I will say that there is still considerable variability in English, even if one is just examining English in the United States. There are regional, ethnic, and racial differences, as well as differences among age groups and different socio-economic groups. There is nothing wrong with this, and in fact, it's a good thing. This makes our language rich!