Final answer:
Macbeth's desensitization to death, coupled with existential crisis, explains his muted reaction to Lady Macbeth's demise. He reflects on life’s futility, revealing his inner turmoil rather than traditional grief.
Step-by-step explanation:
Macbeth's reaction to his wife's death can be explained by his desensitization to tragedy and death, which has developed over the course of the play. At the news of Lady Macbeth's death, Macbeth reflects upon the futility and insignificance of life rather than expressing traditional grief or sadness. This is embodied in his famous speech that includes the line, 'Life's but a walking shadow, a poor player.' His reaction is not solely due to the anticipation of her death or his preoccupation with the approaching army, but rather a deep existential crisis that has been brought on by his heinous actions and the subsequent unraveling of his life.