Part of this is because the US prices of drugs, subsidize the development of drugs around the world. Pharmaceutical companies rely on the US market to offset the R&D of the drugs, while then providing other countries with drugs above the marginal costs (which is still profitable). In this scheme, the pharma company benefits (they increase their profits) as do the other countries (they get cheap drugs). The loser in this arrangement is the US consumer who gets to pay high costs so everyone else can have ground-breaking drugs at low cost.