The billed numbers are almost completely made up. The insurance company (Medicare in this case) will only reimburse up to a set amount.
The reimbursement is calculated as min(billed_amount, allowed_amount). If the facility accidentally bills less than the allowed_amount, they get less than they could have. So to make sure they get 100% of the possible payout, they bill extremely high numbers to insurance.
It's a dumb system, but it's something you have to keep in mind whenever someone talks about how much things cost in the US system. With expensive procedures, products, or drugs, virtually nobody ever pays the big number. It's just a placeholder to make sure insurance payouts are not left on the table.