Additional context:
Native speakers of my mother tongue do not all understand each other due to some pretty extreme dialects. Now that I’m in Europe, I’ve noticed multiple instances of people sometimes not understand the dialect of someone from a village 10-20 km away…
In contrast, for example most American, British, and Australian people can just… understand each other like that?? I never thought much about it before but it’s pretty incredible
Edit: thanks everyone, and clearly I didn’t think of certain parts of the UK when I was in the shower and thought of this…
I would rather guess colonialism. Germans living 150 km from each other not understanding each other is because their languages were organically evolving from some 1000 year old protolanguage with barely any communication in medieval times.
The reason the world speaks English is because a relatively small group of speakers from within England colonised the world and kept communications up with those past colonies to this date.
India or the US didn’t have as much time to diverge from old colonial English as Bayern had time to do so from proto-German. Add to it that a sizeable chunk of the colonies are still Commonwealth.