For example, why do we have so many emergency services numbers? NZ does not even have the same one as Australia.
I think we have 111 because it was the fastest possible number to dial on the old rotary phones that went from 1,2,3,4,5,6,7,8,9,0 counterclockwise around the dial (US was the reverse).
But once the rotary phones were gone.....no physical reason for any particular number except perhaps to repeat the same number.