It's the whole "technically a working uniform" thing that keeps them from being legal in town.
I agree, a suit and tie, regardless of if it has ribbons or not SHOULD be OK for out in town, but I am not the CNO. Look at it this way, what's the difference between me wearing my AWGs sans ribbons and someone who has no ribbons wearing them as "Service Greens".
It may be hard for the current crop of MIDN/ENS's to understand, but I had NOTHING on my uniform when I was commissioned. Zip. Zero. Nada. ENS bars and a name tag. NOTHING.
My proposal to make them "Aviation Service Green" would solve that issue of "must have ribbons to wear in town".
Historical photos show them being worn with ribbons in the 1940s/1950s FWIW.