My theory on why Carlsen offered a draw.
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I could take the easy way out and day that Magnus thought he had no way forward, but here is my hot take.
Magnus knew that Fabi had close to no time left. He knew that his position was not winning. He knew his only chance at winning is if Fabi made a mistake in time trouble.
He did not want the World chess championship to be decided in time trouble for the classical portion, so he offered a draw to be sportsmanlike.
