Re: It's not "why", it's "how"
@fnj: Given your very clear explanation (no sarcasm), I'd still say Trump will make it as President on January 6th. I can't see the US electoral college announcing Trump as President elect, but then choosing Clinton as actual President early next year - a possibility I think you're alluding to.
Has such a swerve ever happened before in US history? Could it really?