I’ve met lots of people who crashed and burned being in the military. Too much freedom and not enough discipline were the most common reason given.
Some people need to experience the school of hard knocks first before they get serious about college. They just took a different path to finally get their degree.
My first NCO showed me his first set of grades from colleges after he got back from Vietnam, 0.6 GPA. 15 years later got serious and got his BA. He was working on his masters when i met him.
Some smart kids never learned how to study. Go to a difficult school where all the kids are smart and don’t do well.
Some people need an external motivation for them to make it through. Once they are told they can’t make it, that is the fire,motivation, they use to make through. Heard this mostly from academy graduates.