My own experience is that it's a generational thing:
My father-in-law joined his regt from Sandhurst in 1938 - by 1941 (aged 21) he was an acting Major in Burma, and left the Army as a Major, and was always known as Major Bloggs. My father left Dartmouth at 18 in 1951, and retired as a Captain. He never used his rank again. His boss discovered he had a CBE and told him to re-print his business cards with it on!
My FiL had a tough and nasty war, and left with only campaign medals - his rank was the only sign he'd served his country. My father served entirely in peacetime, with the exception of some skirmishes early in his career, and the FI in 82, in which he played a significant, but UK desk-driving role.