Because when you call an insurance company, your on hold for long periods of time, just to be told they "don't know" if its covered without the specific billing code, in network, out of network, pseudo network...ect. I have dealt with this first hand, and found egregious errors in billing multiple times. I have saved 1000s in bills/collections over the years by dickind around on hold and basically pitting the insurance companies against the service providers to figure out who fucked up.
Also-for whatever reason there seem to be multiple billing"codes" for the same thing. One may be covered, one is not. GTFO
And best of all-
Prices for all items are "negotiated" between the service provider and insurance companies. Magically, if the insurance is paying a portion, the cost for the bill is much lower-but when its paid out of pocket by the consumer direct, its a fuck ton more? How in the fuck is this even legal?
Using your analogy-
If you drop your car off at the dealer you are suggested what the diagnostic fee will be (which never happens in the medical setting), and then called, and told what the repair cost will be once the problem is discovered. Both of these quotes are provided by the service provider. Again, this does not happen in the medical field.
At the end of the day, the financial side of our medical system is FUCKED. I am not suggesting I know what the solution is, but like all things, the steering power of the almighty dollar effects the system from top to bottom.