If someone's dying wish is to, well, die, then it's probably a good idea to make sure there aren't any necromancers or brain-uploading robots or anything like that around first. They might not be happy to find out later on that something went wrong.

Transcript

Luke: All right, the opposite of suffering. Come on, we can do this.
Han: Sadism! Cause some suffering!!
Chewbacca: Let's just back up a second here. The final step on the Path to the Light Side is sadism?
Han: It's the best idea so far!
Darth Vader: It's all right, Luke. I don't need to complete this Path. I am what I am. I'm ready to make my peace.
Luke: What do you mean? You're so close. You can't die now!
Darth Vader: Help me take this helmet off, Luke.
Luke: But that snippet's in your helmet! You'll die!
Darth Vader: My body is ruined. It's the only way to end my suffering.
Luke: No! I refuse.
Darth Vader: It's okay. I'll do it myself.
Darth Vader: Force Levitation. 16.
Luke: No, mother, you can't! {tries to hold Vader's helmet on}
Han: With that roll, I bet she can.