In such a laissez faire society, why would you "blame" the entity that employs them at some wage, instead of blaming the millions of entities that won't or don't employ them at any wage?

Because the Third Option is being left out: independent living off the commons. This is what disappeared with the Enclosure Movement and thus signalled the rise of capitalism. Wal-Mart is the entity withdrawing this worker from subsistence on the commons, and also partially responsible for the elimination of the commons, therefore they are responsible for "beating" the Commons Offer.