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https://en.m.wikipedia.org/wiki/Decimal_separator

My favorite one is India's tradition of grouping by hundred thousand.

All of the English-speaking areas listed on that page use a period as a decimal separator.

Interestingly, Canada uses both characters as decimal separators, but English always uses a period, and French always uses a comma. That's probably also why Canada also uses a space as a thousands separator, not a comma like the US.

OP's country of Denmark, for one!: https://en.m.wikipedia.org/wiki/Decimal_separator

See the Examples of Use section of that Wikipedia page for a more extensive list.

Denmark is not an English-speaking area though.

I see it as a feature of Euro English, like writing "XIV century" instead of "19th" or saying "actual" with the meaning of "current". Language change caused by an influx of non-native speakers is not a new thing for English.