Most people can't fight it. Fighting a claim, depending on insurance, requires multiple different Doctors recommending the same thing. Sometimes the insurance requires prior steps taken that are unavailable to individuals (I was required to take antibiotic that I'm allergic to before a surgery). Getting into a specialist can take months, and the costs of seeing a specialist are not often covered at all (goes towards deductible), and unless you live in or near a city you may not be able to find specialists you don't need to get a hotel to see (travel expenses and time off work are not covered). Not to mention, if fighting a denied claim rolls over to the next year, everything starts over, even if you have the same insurance it's considered a new policy because it's a new year.
Unless you have unlimited time and money, fighting a denied claim is pretty difficult and goes nowhere fast. That's how the system was designed.
You have sudden onset chest pains and lethargy? Well I see your boobs are nicely sized but the rest of you could lose weight, I prescribe you with diet and exercise and diagnose you with anxiety because you thought you needed to come in. I can prescribe you both control if you continue to be anxious.