I distinctly recall these being the uniform regs, for all intents and purposes, when I was last in on AD in the 80's (Yeah, I'm old.).
I can supply the rationale behind the "you will not run around in utilities" regs. I can't speak for the rest of the Corps, but the Marines in my unit either wore coveralls or cammies as duty uniforms. By the end of the day, we were frequently liberally smeared with grease, synthetic aircraft engine oil, dirt and other assorted crap. At the end of the day, the Marines who lived off base would pile into the car and head for the house. Without those regs in place, tired and dirty Marines would be seen picking up diapers, bread and milk for the old lady on the way home.
Despite the fact that Marines are paid for getting dirty and doing nasty jobs, they are still expected to be neatly turned out when appearing in public. A neatly turned out Marine (Or Soldier, Sailor, or Airman, for that matter) inspires confidence and gives an impression of competence, discipline, and professionalism.