I for one wouldn't introduce myself as the technical director of xxx ltd if I had left. Why should it be different for ex military? If I earn a title in one job then when I change jobs I have to prove myself and earn my position, when I leave - it's gone.
Also many of the (younger) public don't have much comprehension of military titles anyway so it means nothing to them.
Sure I don't want to disparage any former military personel ,especially those who have fought for countries etc they have made a great sacrifice in what they have done, but credit where credit is due.