For the same reason Bush took responsibility for FEMA. The buck stops there.
It isn't Manchin's fault. He is far more "Republican" than most Republican politicians are. He has cut taxes and pushed through some medical malpractice and other legal reforms. As far as I can tell, he is strongly against abortion and strongly against gun control. Back when he was a private citizen with his own business, one local labor union went on strike against him.
He's a good man. I've voted for him before, and if I were still a WV citizen, I would vote for him again in a heartbeat.
Details still seem to be sketchy, but in some quarters he is be being blamed for running with the original "good news", giving the media a credible source, instead of waiting for the company's confirmation.
From what I gather, he apparently got the news from family members. A report on Fox early this a.m. seemed to suggest there might have been an accidentally intercepted or overheard cellphone call involving the rescue people that may have been misinterpreted.
It isn't the governor's fault. The blame game has begun. It's one of the uglier aspects of all these tragedies. Someone has to be blamed, there is no such thing as an accident.