I thought this was an interesting take:
"The reason I did Mandalorian was that Luke had a beginning and an end. There was no middle. It was like making a trilogy about James Bond as a young boy who first became aware of the Secret Service and wanted to be a part of it. Part two was him training to be an agent. Part three is earning his license to kill — The End. No From Russia With Love, Dr. No or Goldfinger. You never got to see Luke as a Master Jedi at the peak of his powers."