I think there's a bit more to it than that. Being mean in a friendly way is sort of a sport, for some people finding a good quip is about the mental challenge of wordsmithing. It's easy, and not all that creative, to say "don't be late" and also with certain people can come across more negatively than just jokingly berating them, believe it or not. It sounds more serious. Something like, "glad you made it, Leland! We were just posting a GoFundMe to buy you a watch." Said in the right way with people you are very familiar with keeps a lighter tone, and less like I'm actually upset (even if I may be.) Not that I'd ever say something like that in a professional setting or to people I'm not actually strong friends with; those people just get a "glad you made it, Leland!"

It's also sort of the same reason shows like It's Always Sunny in Philadelphia are funny. When you're jokingly mean to a friend, you're being a bit of a caricature, an exaggeration. That's part of the fun of it, too. And why it can get a point across while keeping it light.