Largely because the US continues to subsidize medical R&D. Free riding is a good gig if you can get it.
I imagine that dollar-for-dollar a non-profit with the right incentives and oversight could out do the VC-backed leeches driving up prescription med prices.
These amounts are small enough where the U.S. government could pretty easily cover the expenditures. So by your logic, why do we need Silicon Valley venture capital? Why not just have the government pay for the R&D and make the results freely available to everyone?
Either the government is good at allocating capital for high-tech R&D or its not. Whether you're talking about medical tech or computer tech doesn't make a difference.