The other thing to consider here is where drug companies are located and who represents them in Congress. The answer is that most of them are located in NY, California, a few in Chicago, and many in NJ. Almost all represented by Democrats and heavily populated by people who either work for the pharma industry or are reliant on the pharma industry.
Any change that results in reduced profitability for drug companies is going to hit all of these Democrat-represented areas hard. Going to a European-style system would turn NJ in particular into a Detroitesque ghost town.
So you have a rare situation here where the Democrats who represent these districts are duty-bound to represent their constituencies and defend the drug companies.