What makes you call someone Mr. or Mrs. Ms. so and so as opposed to their first name?

It does have a purpose, one that has largely falling away and not to our best effect using the honorific title such as Mr. Ms. Mrs. is a way to keep social distance between people as a default, not everybody is going to be your friend right away. So why do that salesman thing of call me Bob! Inducing a false sense of familiarity, thus perhaps inspiring trust that should not be given.

By staying formal in one’s address you’ll also avoid personal or private subject matter, or even such things as religion and politics. It is a buffer, an Insulator. But like other tools only works when many people are using it.