This would upset the whole concept of discounting group coverage. The concept requires a group that would tend to have a broad range of healthiness. It's cheaper because you've included healthy individuals in the group. And it's cheaper because administrative and selling expenses are lower. A single group insurance sale could take the place of hundreds of individual sales.
Health insurance can be quite complicated.
And it's been made more so in recent years because of different theories on containing health care costs. At the traditional end of the spectrum, you can get fee for service coverage. Within policy limits, this type of insurance pays for whatever medical care an employee gets. Employees may have little choice as the HMO makes many of the decisions about how care will be rendered. Many HMOs are fine institutions, but some cost containment practices have come under serious criticism.