The problem is when the chain of supply and demand grows longer and longer (i.e. covers more distance in terms of culture, national borders, multinational markets, etc), as it does today. In the modern era, what if Henry Ford's factory was in a third world country? There would be no shortage of first world consumers of Ford's products, so in that scenario there is no capitalist incentive to raise the workers' wages. Especially since the first world consumers are buying the products for the very reason that Ford is paying wages impossibly below first world pay scales.

This scenario is also not without precedent, for what it is is the isolation and exploitation of one population in favor of another population, which is a colonialist scenario (as opposed to a Marxist scenario where classes are stratified in a single society). In such a scenario, nothing capitalistically motivated will come to the aid of the exploited population until a very long chain of supply and demand has been unwound.