iOS 10/macOS Sierra: Merging Faces between iPhone and Mac
With their focus on privacy Apple have deliberately made the decision not to sync certain information between devices.

They have documented this in a Knowledge base article called Use Photos and iCloud Photo Library on multiple Mac computers.


  After you sign in, these items appear in the Photos app on all of your
  Mac computers:
  
  
  All original photos and videos
  All folders and albums
  Smart Albums
  Keywords
  Memories
  Key photo selections
  
  
  These items are available only on the Mac where you created them:
  
  
  Books, cards, and calendars 
  Slideshows 
  Keyword shortcuts
  Unused keywords 
  Last imported album (this album contains photos you most recently imported on a specific Mac)
  Names and faces in the People album