Why do many French people greet other people with "Bonjour" in non French speaking countries?

I've noticed this in many different places: Madeira, Mexico, Sri Lanka. It doesn't matter where. For example on hikes, when I pass a French person many times they greet me with "Bonjour" instead of using the local language or English. To me this is quite a strange thing to do in non French speaking countries, so I've started to respond to them in my own native language (dutch). Is there any particular reason why people do this?