All names have times when they are popular and times when they almost disappear. Some goes away but most become popular again in a generation or two. Do not forget there are other countries in the world where some of these names are still alive and well.
Surprisingly there aren’t many celebrities named Duncan. This is Duncan I, and he was king of Scotland from 1034-1040. Remember “King Duncan” from MacBeth? He was the basis for the character.
All names have times when they are popular and times when they almost disappear. Some goes away but most become popular again in a generation or two. Do not forget there are other countries in the world where some of these names are still alive and well.