One of the challenges is that insurance companies insist on only paying about 30% of a medial bill.
The end effect is that in order to actually get paid for a $100 item, the retail bill price has to be $300.
People who don't have insurance are in a tough position, because they are billed the $300 and don't have access to the discounts.
Some hospitals attempted to fix this problem by offering to make the pricing more equitable for all - and the insurance companies refused to go along with it.
Frankly another (insurance) reason is that insurance companies routinely refuse to pay a bill the first time - just reject it. If it comes in a few times, then they pay it. It is their method of holding onto the money longer.