I used to work for a private health insurer (in the US) and our "group" coverage was offered to businesses of 2 people (i.e., a founder and one employee). At that time, at least, sole proprietors were in the "individual" coverage category, but there was talk about changing that.
We tried to get insurance ourselves, and then worked with a family friend broker, and failed both times. We could get coverage for three of us (although my daughter would have exceptions in the contract), but not for my wife. I was 28 at the time.
We're "lucky" in that we had COBRA coverage from a Maryland job before we moved here. Now that COBRA is expired, our MD insurer is required by MD law to offer us a group policy. It's decent coverage, but at almost $1000/month it only covers my wife and the kids. It would be another ~$600/month to add me.
The problem isn't just that health care is expensive. The problem is that it isn't available to many otherwise viable founders. You can be turned down with shocking ease by private insurers; no exceptions, no recourse except a multi-month appeals process that is no more likely to get you covered.
The financial drag isn't the issue for us; the uncertainty is.