"unless you have obvious problems" is doing a _ton_ of work. Most people _do_ have _obvious_ problems. Their weight, their cholesterol, their alcohol use, and on and on.

Saying "if you're healthy you shouldn't worry about your health" is a meaningless thing to say. The point is that most people _do_ have obvious room for some kind of health improvement, and as other commenters have pointed out, if it's not in the clear "this will help me live an additional N years" way, then very likely it is in the "this will make my life suck less as I age" way. Eg; Being able to walk up a flight of stairs without getting deeply winded.