Why do units have issues with keeping soldiers late at work while not doing anything?

I always used the "train to standard not to time" mentality. Many days I would release my platoon early. Rarely did I keep them past 1700 unless we had to do something that really required us to stay late.

My policy was if you have nothing to do, do it somewhere else. There would be times for long hours, but only if required.

Units being held past their normal release time has most likely been going on since the Roman legions, while there are many good reasons to keep a unit later, important info that needs to be distributed, last Sensitive item not accounted for, changes in start time for the next work day, required issues not taken care of during the duty day etc, etc. There are far more example of poor leadership either forgetting there are troops sitting down at units waiting to be released to eat, see their loved ones, take care of important purchase that need to be done before places close. How many times have First line leaders sat through speeches /Death by power point/ a Pet Peeve debate and assorted other "I LIKE TO HEAR MY VOICE" Oxygen depletion sessions. Some "leaders" either through purposeful acts or because they get distracted have troops standing by only to be told regular 1st call, PT, vehicle and weapons PMCS which creates poor morale when done consistently. Maybe as the leaders go up through the ranks and work longer days they forget the troops with get their long days down the line when the get more rank. As a PSG I had to be in the Barracks no later than 0500 and many times long after the Troops were released I was in meetings at 1900-2000 about nothing only to return at 0500, This along with weekend/Holliday visits to the Barracks to check on the young's to make sure they take out the trash, don't burn the Barracks down or declare war on a neighboring company involving start clusters, grenade sims and assorted pyro and rifles.
My belief was that Troops will always work long days due the the nature of their jobs so there is no reason to make them stay for "NOTHING" as they will already be staying for "SOMETHING" down the line.