"Wouldn't it be better to let such cures evolve through random selection?"
Natural selection is not random.
"I am intrigued as to the motives scientists might have for interfering with such natural processes."
Saving lives? Maybe of someone they love?
Saving the lives of people we love sounds good to me as well.
It seems strange that human beings would have such motives-- as natural as we are.
I thought our genes were more selfish than that.