They are!
Which is why North American English is more like 12 languages, going by your chart.
View attachment 400497
Though, -really- these are all just very broadly defined Dialects of English, just like Scots English. Where the vast majority of words contain the same intentions, meanings, and definitions, but there's some significant drift in which words are more commonly used, local phrases, pronunciation leading to accents, and unique terminologies.
Like "Bubbler" instead of "Water Fountain". Or the regional agreement on Soda, Pop, or Coke.
View attachment 400498
This is because:
1) North America is massive
2) Different languages influenced different areas based on specific cultural diaspora
3) Mass media and public education slow the drift significantly
Without newspapers, television, and movies there'd be a -ton- more lingual drift in North America after 500 years of settlement.