I'm pretty sure most people with an existing condition would prefer not to have it at all than to cost insurance companies more and have that covered.

It's not a free lunch. They paid the admission fee with their health.

Regular wellness checkups are also not a free lunch. They're priced into the policies. You absolutely can insure against regularly consumed services, as long as the premium is enough to cover it and to do the underwriting for the unexpected expenses. Look at dental or vision insurance. The vast majority of what they cover are regular wellness visits.

Putting that aside, free wellness visits are also in the interest of the insurer. It's far cheaper to prevent disease or to treat it early than it is to deal with it later. Those savings from this so-called "free lunch" ends up right back in their pockets.