The reasons for the failures of the USA health care system are complex. Given decades of failure those with leadership positions (hospitals, doctors, politicians, insurers) all have failed. Drug companies I would put below those 4 (they mainly just take advantage of lots of weak politicians to buy bad policy, for the country, that favors drug companies). Exactly what percentage of the failure to put at each groups footstep is hard to judge, but the collective failure is obvious. It is something we couldn't afford in 1980 and the damage to us grows every year. The USA health care system costs twice as much as other rich countries and the results are mediocre. Big business has some responsibility but mainly they just have ignored the problem and not done anything to help (versus actually intentionally sustaining the broken system). Voters have a huge responsibility for decades of re-electing those that maintain the broken system.
Related: International Health Care System Performance - Overview of 5 Nations Health Care Systems - USA Health Care System Remains Broken, Neglected