Why didn't Obi-Wan Kenobi kill Darth Vader?

[Jon]

After Anakin Skywalker turned to the dark side and becoming Darth Vader after he lost his fight with Obi-Wan and getting burnt so badly which he was later saved.

In his next fight with Obi-Wan in the Obi-Wan Kenobi, Obi-Wan had him beaten but didn't kill him. Why didn't he? When it was clearly obvious he's gone over to the dark side completely and he wanted to kill Obi-Wan too.

 

[Flint]

Anakin Skywalker - Darth Vader is his best friend. He actually taught Anakin everything he knew, he's more like a father to him. It's going to be very difficult for him to kill him even though Anakin wanted to kill him. It's the only sense I can make out of what happened between them.

 

[Mimi]

He couldn't bring himself to kill his best friend twice. He blamed himself for years for killing him without knowing he was never dead. This why he couldn't kill him again.