[shabda]

Most of chronic diseases progress slowly and have no external signs in early stages. Most of them are also much simpler to treat in early stages.

> I fail to see how screening of healthy, relatively young, people would be "data driven".

So just by looking at yourself, you don't know if you are healthy, only that you look healthy. The tests are to ensure that you are, and to give you time and flexibility of treatment if you are not.