Which explains why we can understand Aussies and Kiwis, but a random Nigel from the UK would have a speech that baffles. It boggles the mind how two people from different corners of London have different accents. Not to mention Manc vs Scouser vs the myriads of tongue-twisting nasal hiccups uttered all over them Shires. It's like they almost take pride in differentiation. Throw an international party and the two UKia…
Also, IIRC, the colonies tended to have a commonality in heritage of the colonists, too. E.g. at one time, Australia had a "large number" of criminals, there are quite a lot of Dutch in NZ -- there are large parts of NZ with very strong Scots heritage -- New York is famous for Irish heritage, other parts of USA are famous for German, etc. The UK hasn't really had the same homogenisation outside the big cities.