What I can't quite figure out ...That's simple to figure out, and it is not specific to hospitals. Some purchasing manager says "hmmm ... I'm paying $100,000 per year for this product. But I can buy it overseas for only $20,000". Score!
At the end of the year, that purchasing manager writes a report to his manager saying something like "saved the hospital $10,000,000 by optimizing our supply chain". Or some such.
How much some random operation costs doesn't factor into his decisions at all. That's not what he's being compensated for.
The only way this mindset changes is if top management insists on it. But usually top management is constantly pushing to cut costs. Their bonuses depend on it.