I can’t vouch for all East Asian countries, but in Japan, it’s a matter of formality. When you meet someone, you always refer to them by their family name and an honorific. (Like we would say, “Mr. Smith.”)

Once you start to get more friendly and familiar with an individual, you’ll move on to more intimate honorifics, until you’re allowed to call them by their direct first name, no honorifics. That’s a sign that you’re very close with someone.

It allows people to refer to you without being too direct and familiar until you’ve gotten to know them well. And you can tell what relationship two people have by what names they use to call each other. Heck, really close friends will probably make up nicknames for each other too.

When I was in the US military, it was kind of the same mentality. Everyone was referred to by rank and last name only. As you got to know someone of the same rank or lower than yours, you could refer to them by last name alone, no rank required. But only the closest of friends would refer to each other by first name.