Why do the innocent suffer?

On example of the innocent suffering is in Alma 14. Those people who
believed the word of God taught by Amulek and Alma were thrown into a
fire.

10 And when Amulek saw the pains of the women and children who were
consuming in the fire, he also was pained; and he said unto Alma: How
can we witness this awful scene? Therefore let us stretch forth our
hands, and exercise the power of God which is in us, and save them
from the flames.
11 But Alma said unto him: The Spirit constraineth me that I must
not stretch forth mine hand; for behold the Lord receiveth them up
unto himself, in glory; and he doth suffer that they may do this
thing, or that the people may do this thing unto them, according to
the hardness of their hearts, that the judgments which he shall
exercise upon them in his wrath may be just; and the blood of the
innocent shall stand as a witness against them, yea, and cry mightily
against them at the last day.