Except if you go in for a major procedure, you don't know what you'll end up needing off that price list, and often, neither does your doctor. So even if providers were perfectly transparent about what a procedure would cost (and it's well-established they're not - just try calling and asking for prices) the nature of the service being purchased is that you sometimes don't know exactly what you're buying until it's too late to change providers.
A few years back I broke my leg and went to the hospital. Halfway through the process I was offered a couple of Vicodin, which I would later be billed $1,000 for. Was I supposed to haggle about them with that, or take my xray and hobble out down the street to someone who would sell me vicodin cheaper?