Why Did Kratos Say No to Odin?

Kratos said no to Odin because Odin's peace came with a price he wouldn't pay, from a god he had every reason not to trust. The deal was that Atreus would stop searching for Tyr, and Kratos would let Odin decide what his son could and couldn't do. The game never has Kratos explain himself. He just stands up, looks Odin in the eye and says no. (God of War Ragnarök)

The offer at the door#

God of War Ragnarök opens three years into Fimbulwinter, the long winter that began when Kratos killed Baldur. One night the roof caves in and Thor is standing outside. He comes in with mead and sits across the table from Kratos. Then Odin knocks. (God of War Ragnarök)

Odin plays the friendly old man. He calls everything that led to the winter a set of misunderstandings. The deaths of Thor's sons Magni and Modi he waves away as self-defence, and he is openly scornful of them. Baldur was different: Baldur was valuable, and that is a debt Kratos owes. (God of War (2018); God of War Ragnarök)

Then the terms. Odin will forgive the debt and keep Freya from hunting them, and they can keep Mimir, whom he knows they have. In return they leave the Aesir alone, and Atreus stops searching for Tyr, the Norse God of War, whom Odin says is dead along with his old ways. Kratos turns to look at his son. He hadn't known. (God of War Ragnarök)

Mimir's warning#

Odin and Mimir trade insults across the table, and Mimir answers with a warning for Kratos: if Odin tells you snow is white, he's lying. Mimir knows. He was Odin's adviser, and Odin kept him in a tree and tortured him for over a century. (God of War Ragnarök; God of War (2018))

Kratos stands and says no. Odin leaves, telling Thor not to take all day, and Thor smashes Kratos out of the house with Mjölnir for a fight across the frozen lake. (God of War Ragnarök)

Why Kratos refused#

The game leaves the reasons for the player to read, and these are ours, drawn from what the games show. (God of War (2018); God of War Ragnarök)

• Odin's word meant nothing. Mimir had just told him so, and Kratos had spent the last game hearing what Odin did to Mimir, the giants and his own family. A promise of peace from Odin was not peace. (God of War (2018); God of War Ragnarök)
• The price was Atreus. The one thing Odin wanted was control over Kratos's son. Kratos had spent the 2018 game learning not to be the kind of father Zeus was to him. Agreeing to bind Atreus to Odin's terms, without even asking him, would have been the opposite. (God of War (2018); God of War Ragnarök)
• Odin was after the boy. While Thor and Kratos fought, Odin stayed behind with Atreus, told him he wasn't interested in Jötunheim any more, and invited him to Asgard. The deal looked like it was about Tyr, but Odin's real interest was Atreus, whose gift for ancient languages he wanted for himself. (God of War Ragnarök)
• It wasn't a choice of war. Saying no didn't mean Kratos wanted Ragnarök. He spends much of the game trying to stay out of it. (God of War Ragnarök)

Was he right?#

Everything that follows says yes. Odin went straight to Svartalfheim, disguised himself as Tyr, and let Kratos and Atreus rescue him from his own prison. Living among them as "Tyr", he advised against fighting Asgard while he worked on Atreus. He drew the boy to Asgard to rebuild a mask that he believed held the secrets of creation. When the dwarf Brok saw through the disguise, Odin stabbed him to death. (God of War Ragnarök)

That murder is what finally pushes Kratos and Freya to take the war to Asgard. In the end Atreus chose his father over Odin and broke the mask, and Odin died refusing to give up his obsession. The Ragnarök ending explained covers the final battle. (God of War Ragnarök)

Our reading is that the one-word answer is the most Kratos thing in the game. He doesn't argue or bargain. He refuses to trade his son's freedom for his own quiet life, and the story that follows is about him finding out what keeping that promise costs. (God of War Ragnarök)