For a lot of years after we got out of the army, William B. McKechnie III was my best friend. Bill is dead now, but for all the years we knew each other, Bill refused(?) to tell me what the "B" in his name stood for. One of his forbears, he said over and over again, had added the middle initial because rich people had middle names and he wanted to ally himself with the rich folks. So Bill's "B" stood for nothing at all. It sounded swanky.... and I never quite believed him.
Nowadays, the shoe seems to be on the other foot and people are entrenched in the use of hyphenated last names, names that recognize both parties on the parental pillow ... or acknowledging the names of both parties in a same-sex marriage. Harry Smith-Jones or Sarah Cymbal-Sassafras or some such.
And I still don't quite believe my one-time best friend's explanation.
If we wait long enough, maybe things will get reduced to the usage of various island or impoverished nations where just one name suffices.