Are you sure? I think they say zed in India, Pakistan, and Bangladesh. That’s quite a few English speakers.
> Population > 2018 estimate > 1,352,642,280
> Official languages > Hindi > English
As a starting point, this source lists about 128 million people: https://en.wikipedia.org/wiki/List_of_countries_by_English-s...
It probably started with the popularity things like Sesame Street and Dragon Ball Z (Dragon Ball Zee).
However, interestingly, the one time everyone uses "zed" is when we acronymise the country name -- NZ, or N-Zed.