One major reason they would not enlist in costume is the reason they put that costume on in the first place: to protect their normal identity from the consequences of their superhero ID. Starman simply does not have the restrictions that Ted Knight does, especially as a member of the armed services. Orders, chain of command, officers privileges and more: none of that applies to Starman.
The whole 'auper-technology never changes anything' trope comes down to one major reason: if you follow the natural and normal consequences of these hyper-inventions, you quickly wind up with a world where you are incapable of telling stories that people can relate to. They have no real foundation for understanding a world where everything is powered by stellar radiation, for example. It's just something not to worry about.
The 'people are not ready to use x' idea, though, is the best one to use. Give the cosmic rod technology to anyone who is not a pure-hearted altruist like Ted and they'll be ruling the world with it next week.
You can also look at it like this: the writers in the 30's and 40's were taught and trained by men from the 19th century. The late 19th century really loved the idea of the 'Great Man' theory of history, where history was made not by a natural confluence of events but by the individual actions of men whose intelligence, wisdom, will, and strength of character forced events to play out as they wished. Superheroes are all over that view of the world; they can be trusted since they are Great Men, a breed apart from the corrupt, venal and petty nature of most people.