In other words, demand is inelastic.
And, most people can't afford to pay 10k or 100k out-of-pocket. So, it's not like managing your household budget. The funds have to come from somewhere else (insurance).
Also, healthcare is not easy to evaluate for a layperson. If my doctor says that I need 'procedure X', I'm relying on their expertise. Healthcare recommendations are not fungible products. If I'm buying a car, I can read reviews about the different models, reliability, etc. But my doctor's recommendation for me is highly specific to my personal health history.
So, for a lot of healthcare spending, it's not me that's choosing a medical procedure. Instead, I'm choosing to trust a doctor's recommendation. The doctor is the one that's recommending the procedure.