We asked the same question. The answer is somewhat political but this may help to explain:
When thermography was first explored for breast imaging, it was viewed as competitive to mammograms. It was tested and evaluated to see if it was safer and more diagnostically accurate than mammography. These comparisons should not have been made, as you can not compare tests of physiology and anatomy.
In particular, when thermography was tested on younger women, thermographic abnormalities were detected many times but mammograms did not detect any tumors. The results were considered false positives. The more patients of younger age screened with the so-called false positive, the more suspicion was placed on thermography. Years later, in re-call studies, a large percentage of these women had developed breast cancer or other breast disease, in the exact location of the abnormal false-positive thermogram, thus validating its early warning role. Thermographys only error was that it was too accurate too early and the results couldnt be corroborated at the time.
Secondly, thermography was being used in sports medicine, dentisty, podiatry, chiropractic, orthopedics rheumatology, and neurology in a variety of support or adjunctive diagnostic roles. It was soon realized that thermography could clearly, objectively, and easily demonstrate the physiological component of pain and injury, especially to the spinal column, due to car accidents, job injuries, and a host of other tort related law suits. Everyone involved had benefited from these positive test findings, which could be clearly shown to a jury. Everyone that is except the defendant insurance industry.
Needless to say, the insurance industry in the United States placed an all-out effort to diminish the value of thermography in courts of law due to high litigation costs. Eventually, lobbying efforts at the AMAs House of Delegates and at Medicare, brought about the removal of thermographic coverage by most insurance companies and the greatly reduced utilization of thermography in the United States. This was most unfortunate for the patients who could clearly benefit from thermal imaging.