Nation-sized leverage. The same reason why equivalent pharmaceuticals are cheaper elsewhere in the world.
The actual facts are in support of the posters point: https://www.abpi.org.uk/facts-and-figures/science-and-innova...
But your example is a real occurrence of abuse under the US system.
The first world has successfully encouraged the drug makers to sell their product cheaper in the third world. If you look on wikipedia drug articles you'll see the price for the generic in the developed and developing world.