Re: It's not "why", it's "how"
I find this good comment, just one thing to add. In this elections Democrats cannot blame third party candidates for the loss in most states, including Michigan. The thing is that, just as Stein took votes from Hillary, Johnson took votes from Trump (and Johnson had 3 times as many votes as Stein). So in my opinion, had third party candidates been forbidden, Trump would have added more or less all 3.6% from Johnson, and Hillary could have counted on Stein voters - 1.1%, so the difference would have been even bigger for Trump - which I find amazing but that is how I see it. Hillary could consider herself practically lucky that Johnson and Stein were in the race, because Johnson took more votes from Trump than Stein from Hillary.
But I would say that discussion about third party candidates is missing the point. If Democrats cannot win against Trump who, in my opinion, at one time or another, insulted every group of people in America, then they have only themselves to blame and not Stein, Johnson or Facebook.