Allan Poe or Poe?

[5jj]

There is some information here, but I don't think it really answers your question:
Middle name - Wikipedia, the free encyclopedia
also:
Jack and Jill: A Study in Our ... - Knihy Google

[ohmyrichard]

I am not a teacher.

Various reasons, I guess. It's not a universal cultural thing. Some people are proud of their middle name, sometimes because it is part of a famous name. We have George Washington Carver and John Wayne Gacy, to name two (who couldn't be more different otherwise). There seems to be a tendency to use middle names in the American South---Jerry Lee Lewis, Billy Bob Thornton---though those start to look like double-barreled first names after a while. Sometimes the mother's maiden name carries a cachet---Mary Wollstonecraft Shelley. Sometimes it just sounds good---James Earl Jones. Pity me---I have a first initial, like T. Boone Pickens.

Wonderful explanation! Thanks a lot.
Richard