It’s a little strange that a dedicated button would be needed to switch between them, especially when the math to convert between them is so simple.
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.