The implicit assumption in libertarian perspectives is that all parties are rational and have similar levels of information. In healthcare, this is simply not true. The average person isn't capable to judge what is and isn't necessary for them (outside of the small amount of very routine and elective care).

Likewise, if a hospital hands you a bill for 30k and you need help, are you really going to be able to negotiate and find a better price?

Healthcare is fundamentally an in-elastic good.