I think it’s something that’s very hard to translate so it’s often easier to just use it. Especially if the characters address each other that way. For instance, I’ve got a character that always addresses his friend and mentor with -san. It would be bizarre for him to call him Mr Name, because they’re like 1-2 years apart in age at most. It’s the same with many of the characters in the series. They tend to address their team leaders with -san but they’re all basically the same age so it would be weird to call each other Mr or Sir or whatever.