Unlike Moore, who was guilty of nothing, Blankenship went to prison for the deaths of 29 miners. This guy ensures Manchin wins reelection handily.
Moore in Alabama had lots of stuff thrown at him, and most of it stuck because he lacked the charisma to respond effectively. In political races, like it or not, ability to vocalize a good and effective response is a necessity.
Family members of the victims and surviving miners would likely appear in ads for Manchin detailing the horror of that disaster. Whether or not Blankenship was personally responsible is irrelevant as far as electoral success in that scenario - that is simply a devastating dynamic to achieve victory.