The iPhone has about a 56% market share in the US, compared to a 26% market share in Europe (with the UK being the outsider with 52% market share).
That makes a huge difference: in Europe it's very unlikely that everyone out of any group of friends has an iPhone, making Whatsapp, Telegram etc the goto solutions for group messages.
Apple is also huge in Japan, but I don't know what kind of chat apps are used there.
I'm from EU and it is a thing. I use iMessages whenever the other side has an iPhone. In my social circle, it's about two thirds. But it is also true that many people who have an iPhone still use Whatsapp or Messenger as the default communication channel even if the other side has an iPhone as well.
Its certainly not the default in Australia. Only a few people I know have iPhones. SMS is always the default messaging app unless you have added the person on something else which is a bit of a mess between different services.
That makes a huge difference: in Europe it's very unlikely that everyone out of any group of friends has an iPhone, making Whatsapp, Telegram etc the goto solutions for group messages.
Apple is also huge in Japan, but I don't know what kind of chat apps are used there.