To be fair it is kind of their business just in a very indirect and invasive way.
Your health affects your performance, your health affects their health insurance, disability, and life insurance premiums.
This means that as far as the faceless entity of a business goes your health is its concern. Now whether we agree to just accept that or not as a whole other story.
On a personal level I wouldn't mind my employer being more involved in my health, not invasively or privacy violating like the above. Providing access to nutritionists or trainers, supplementing a gym membership under the agreement that I actually use it. Making exercise equipment and group workout sessions available. Things like that.