Where do people get these ideas? Libertarianism is all about freedom, including the freedom to cooperate with others.
For example, a baseball team is all about voluntary cooperation for a common goal. Nobody is forced to play. Baseball has nothing whatsoever inconsistent with Libertarianism.
What Libertarianism lacks is forcing people to conform and cooperate.
But, given things such as the historical existence of company stores/scrip and the things mentioned in Upton Sinclair's The Jungle, I find such beliefs to be overly optimistic: we already have historical proof that companies will fail to pay workers with real money and will sell unsafe food to the public unless forced to do otherwise by government intervention.
Companies have less "freedom" now than they did 100 years ago, and we are better off for it.
Those people would have a stroke if they knew what Libertarian used to mean in the 19th century... ;)
As for failing to pay workers, or selling unsafe food, that is against Libertarian principles because Libertarianism requires government to enforce contracts, and does not allow hurting one's customers.