Great thread! I am not sure I have an answer, but I can say what I have observed from my own personal experience.
1) They tell you that tests are expensive, and if they run them, they don't run complete panels. If medical health is provided not as a basic human right but as a privilege (and here the issue gets more complex than insurance only, so it's not just an American problem, though here it may be more visible), then you don't want to pay the labs, you want to pay the pharmaceutical industry. They're the ones that, ahem, hold classes in exotic islands for their doctors... so yes, tests are expensive, but also if you make a "diagnosis" that keeps the patient on lifelong medications, which after some years require medication #2 for the side effects of medication #1, then the doctor is feeding Big Pharma, saving Big Insurance's money, and therefore getting their little perks. Most honest doctors *will* tell you that they get incentives to act this way, which is how I learned about this. You make the patient live with the disease rather than trying to shake the disease off them. Chronicizing is monetizing.
2) Misinformation/laziness/sheer ignorance/degrees granted where the students should have been given a plow to till the land. No specification needed here.
3) The spinning out of control of the "psychosomatic disorder" craze, which I summarize as a great insight gone awry. They finally figured out that the mind can affect the body - which is "duh," if you think about it, since my mind exists because I have certain organs - brain above all - which just happen to be parts of my body. But then this became misinterpreted by people at point 2 as an epidemic of "hypochondria rampans" - which was exploited by people at point 1 to make munny out of, mostly, psychotropic drugs. A quick search in the APA archives will help you figure out how many people in the US use one or more psychotropic drugs. The numbers are high enough that either the whole nation is under the attack of invisible soul-sucking zombies, or simply psychotropic drugs are being prescribed to people who do not necessarily need them. Long story short: if we believe that most people are hypochondriac, why should we test them? Just give them Prozac!
3.1) The latter point is further complicated by how some conditions are simply not or at least badly understood AND may mimic mental health disorders. Autoimmune conditions are a case in point. Many of them cause exhaustion, or altered moods, "brain fog," nervousness, panic attack, weight alterations etc... Obviously, it's easier to assume it's the "mind alone" to cause them, rather than the "mind as part of the diseased body" (which, as you can see, contradicts the principle itself of the psychosomatic hypothesis), as if the patient's "mind" floated around, detached from their bodies. So you don't test for celiac disease because the plaintive patient is just victim of the latest diet's fad; you don't look for lupus / arthritis rheumatoid because the patient is lazy; you don't test for thyroid disorders because the patience is a lazy pig or an annoying anorexic (this is what happened to me). You "choose" to be ill, so why bother? After all, we know that most women are "weird" in the head and blame it on their bodies, like in that times of the month, so how can you trust a woman in pain? Funnily, most autoimmune patients are - you guessed it - female. So you need to multiply the imaginary patient bias by the gender-defined bias.
3.1.1) Which brings us to cultural frameworks. All of the above behaviours are instances of "victim blaming." So long as we live in a world in which we believe no one should receive help because they "brought it upon themselves," we will not receive better healthcare - no, not even those of us which were sc*ewed by our genes.
Sorry, this may be more of a rant than an answer! Hope it is of some use though!