“Instead of saying ‘ma’am’ or ‘sir,’ recruits in these Services refer to their drill instructors using their ranks or roles followed by their last names,”

...the point is that you earn that, calling someone by their name. It suggests a certain familiarity and similarity in status, which doesn't exist for recruits. Once you're properly in and finished training, Pvt So and So is on a lower rung than Sgt So and So, but it's much closer in status than recruit/trainee/whatever the marines call them these days, and Sir/Ma'am/DI.

Military culture is a thing in the US, and I imagine it's similar elsewhere too. It seems absurd to look for recommendations about that culture from people who aren't even familiar with it, let alone a part of it.