So what's the solution ? Require 25 years instead of 20 to get a pension ? Signing bonus for re-enlisting ? Higher salaries ? Better treatment ?
To me a big failure is "enticements". Drawing people in by making promises that have nothing to do with a happy career....things that just spoils them ....then they are either miserable when a promise is broken or get out. Thus the system breaks down at many levels.
Leadership has to find a way to treat individual needs at lower level....because people are individuals, they change as they grow up, emergency needs well of course emerge and a solution is needed.
The one size fits all, everyone is the same leadership is for the weak, the mindless, the self preserving, etc...etc... Leaders lead and have to be smart enough to figure out how to manage individuals and not clones and explain why different treatment at certain times works for all. Sure boot camp is about breaking one down and rebuilding into a clone... that's so they "get it"...but once in past a couple years to 5, 6..... the end of enlistments etc...these people have been subjected to all forms of leadership and depending how good or bad it was mostly determines whether the service will get another chance...and that repeats until a person leaves or retires.
The other killer is the "up or out" system. It hurts on many levels because people have to get varied experiences (moved around a lot as Garbler mentioned) or forced out early in a career because of many reasons that aren't associated with performance. I understand that is was developed because of the poor performance of the pre WWII military...too many retired on active duty... but the USCG quickly realized that in tough times they needed programs to keep some of that experienced talent around. The problem is, many will not serve in a reduced or limited or relocated capacity so it seems only partially accepted. Some are just bitter for being forced out in their prime.
For me, one thing that really hurt was the grinding down of respect for people in uniform. Not the public, just times a'chngin. I used to joke how back in the late 1800's a Major or Lieutenant Colonel could be a territorial governor. They had almost unlimited powers vested in them. By the time I retired, I couldn't get a pencil without going through 2 or 3 junior people, a couple of forms and told it would take 2 weeks. When I joined and was assigned an investigation....I would do it, written on yellow legal pads and when done, give it to a yeoman (basically a clerk) to be typed up and submitted up the chain of command. By the time I retired, I had to type the thing up myself...but instead of it disappearing...it would get emailed back and forth for days with some senior guy tweeking, correcting, not agreeing, etc...etc... I signed it...get over it and send it up the line ...fortunately word processing took care of spelling and basic grammar so that was not the issue.
Then there are all the "social" issues that takes important time out of "the good stuff". People are offended at the drop of a hat these days. So the military being the best social science test bed, program after program requires personnel to sit through training that I agree can help..but way too many were quickly brought online and not well thought out to do real good.
Bottom line is society is way more complex than it was years ago...on all levels...so there are no easy answers. People haven't changed all that much over the years, but society has expected us to all conform to a neutral center. Many changes have been really good, others not so much and have cost money and time that we will never get back...and a lot of good people hit the road because of them.