I think you neglect the motivation factor. Hard data that can be quantitatively tracked is motivating for many. Think of the fitness tracker market. It’s huge. For myself, the tests served as a wake-up call in a way that knowing I was 10-15 lbs too pudgy and not the fastest runner was not.
At the very least, good medical care provides information. What the individual does with it is up to them.
I get it. But you can get similar data from the old-fashioned way of measuring circumferences, weight, height, pinch test, etc to get body fat percentages, or the VO2 max approximation tests. The other thing to point out, is the only people getting/doing any of these tests are already motivated enough to give a damn.
Yes, medical care should provide information. There are lower tech and cheaper ways to provide actionable information. But like you said, it's up to the individual. Either the will is there or it isn't. If someone knows they would benefit from the visual representation of a scan, they can ask for one. Technically DEXA carries some risk with x-ray exposure if done on a recurring basis.
At the very least, good medical care provides information. What the individual does with it is up to them.