There are probably a dozen things wrong with your body right now. That doesn't mean they're even affecting you. While you may have some type of cancer that is at the absolute first day of detectability, or a bone slightly out of place, or a weird spot on your heart, someone else has a case that is 6 months deeper and needs more dire treatment.
There is zero benefit to society to massively overburden our healthcare system (this is true of any nation) by searching constantly for random problems that may or may not exist.
If there were good reason to do this, you'd have regularly-scheduled checkups, like with colon or breast cancer.