You did not know that large parts of the world default to 12h time?
This is absolutely NOT an American thing. I am not American and have never lived there. I am 58 years old, British and Irish, and lived a decade in Nigeria and a decade in Czechia. I have travelled widely around Europe and can get by in 6 foreign languages.
12h time in real daily life is more common everywhere I have ever been. Only minor subsections of humanity -- military people, maybe -- work on the 24h clock.
Ooh that explains a lot.
24 hour time is used extensively in the UK. For example, all public transport uses 24 hour times here.