Most good doctors know that an accurate diagnosis can be made 80% of the time by performing a clinical examination. Tests are usually done to confirm the diagnosis - and ideally should be used sparingly, and only when called for - when dealing with a complex or rare problem, for example.
Unfortunately, it takes time to do a thorough clinical examination. Taking a reliable history from the patient can easily take 15 minutes. In this day and age of 7 min clinic visits, doctors simply cannot afford the luxury of doing so ! The irony is that the patient's money is then wasted on ordering unnecessary tests.
This sets off a vicious cycle. Most imaging machines provide very high resolution scan images. The radiologist reports these - after all, that's his job. The problem is that even normal anatomic variants are reported , and when patients read this report, they are worried that they have a serious problem which needs correction. An excellent example of this is a prolapsed intervertebral disk seen on MRI scanning in a patient with backache; or a "torn cartilage" see on MRI scanning in a patient with knee pain.
The patient then demands surgical correction for this abnormality , without realising that there is often no correlation between the scan picture and his symptoms. Most doctors are happy to comply - they get paid a lot to perform procedures.
Thus, by refusing to pay primary care doctors for their time and expertise, and forcing them to "process patients " in an assembly line fashion, insurance companies and the government end up spending much more - and the patient is the loser in the long run !