Great question. The answer is quite simple. There is no evidence that body scans save lives. For example, in the 1970s it was thought that doing annual chest xrays on smokers would improve lung cancer survival. So a study was done. It took a group of VA veterans all who were smoking and 1/2 the group got annual chest xrays and the other 1/2 no xrays.
The group that received xrays annually did find lung cancer growths in otherwise asymptomatic people. Although we patted ourselves on the back, did surgery, and gave them chemotherapy, the shocking part of the story came later.
This group did NO better in survival that the group that didn’t get chest xrays. In other words smokers with symptoms of shortness of breath, weight loss, coughing up of blood, survived just as long as the group that was getting annual chest xrays.
Therefore this “screening test” of annual chest xrays did nothing. A good screening test identifies problems early and doctors and patients when aware of the problem earlier can do something about it and improve survival. Otherwise if it finds illness earlier but does not better than no screening test, it isn’t helpful.
Body scans don’t have any evidence of improving lives. An ongoing trial is underway to see if lung CT scans in smokers is better than chest xrays, results will be out in the next few years.
Also, body scans have radiation. A body scan could have radiation exposure equivalent to 200 chest xrays. Radiation, unnecessarily, is a risk factor for cancer as well.