Not because he's the best candidate or that libertarians are now popular with the public, but because media will give him free marketing in hopes the Republican vote is split enough to help Obama.
There will also be a media campaign to build up economic recovery. Already, I'm hearing media reports of manufacturing jobs on the rise, foreclosures down, housing starts rising and unemployment claims at a four year low. What we have is stagnation with some small improvements. America's economy is still the greatest in the world, so you can't keep a good country down, but, we should be growing in leaps and bounds with the potential for energy production. If we didn't have Obamacare and Dodd-Frank scaring businesses into inactivity, those trillions of dollars sitting idle would be actively invested and the economy would boom.
It's difficult to listen to media today without great laughter, but Democrats are betting on American stupidity and that they will the propaganda one more time. Media will present Johnson to the public as a viable alternative to Romney. He is a viable alternative, and I would rather see him President, but if he gets enough votes, Obama will benefit, not Johnson or libertarians.