” For example, they could have killed Adolf Hitler and allowed six million Jews to thrive in Europe between 1939 and 1945. The fact that this never happened suggests that either time machines will never be constructed in our future or that their creators have no interest in saving human lives.”
That’s a rather odd conclusion. If they have the technical skills to create a time machine, maybe they have the wisdom not to use it.
It may be that the rules of the Universe simply forbid time travel even though it ought to be possible in concept.