Did he fear losing to Karpov and potentially losing his hero status in the chess world? His justification for not defending his title was bogus. Draws are a part of chess. He and Spassky played to 11 draws and he was still able to win the championship. He must have sensed Karpov presented enough of a challenge that those draws could be decisive enough to swing the outcome. But if all their games were draws, he still would have retained the title.