Ultimately, Rian Johnson puts theme and character above anything else, so this decision makes sense for his directorial style. While it may have been satisfying to get some resolution between Anakin Skywalker and his son in The Last Jedi, Luke only knew Anakin Skywalker for a brief moment once he removed Vader’s helmet at the end of Return of the Jedi. This Anakin was a far cry from the one seen during the prequels and the Clone Wars, now being left as a frail, old man. Therefore, it may have felt disjointed for Luke to interact with a version of his father that he never truly knew.
In a recent Twitter thread, director Rian Johnson talked about the development process of Star Wars: The Last Jedi. In response to being asked whether he considered using Anakin’s force ghost for a conversation with Luke or Rey, Johnson stated that he did, but chose Yoda instead for the personal connection.
“Briefly for the tree burning scene, but Luke’s relationship was with Vader, not really Anakin, which seemed like it would complicate things more than that moment allowed. Yoda felt like the more impactful teacher for that moment.”
Briefly for the tree burning scene, but luke’s relationship was with Vader not really anakin, which seemed like it would complicate things more than that moment allowed. Yoda felt like the more impactful teacher for that moment.
— Rian Johnson (@rianjohnson) December 1, 2020
It is clear that the theme of The Last Jedi is failure, and Master Yoda was truly the only character capable of delivering this message to Luke. While the Skywalker has learned a lot since his appearances in the Original Trilogy, he still had much to learn. The personal relationship between Yoda and Luke makes the burning tree scene even more poignant, with the Jedi Master being the only one able to show Luke the error of his ways. Having Anakin in this scene may have muddled this and led to more confusion than satisfaction