I think a lot of people dont know what prexisting condition really means in the marketplace. People tend to think of individuals with chronic conditions such as AIDS , tuberculosis, heart failure, etc, or else that people are making excuses and have some minor condition that they can just live with without insurance (like maybe the person has minor asthma and can pay cash for inhalers but not get insurance). But these are really just the tip of the iceburg.
Fact is, insurance will deny you for ANYTHING. Basically any medical condition can prevent you from getting insurance. For me, the fact that in any given year I have maybe a 3.5% chance of requiring a $50,000 hospital stay, means I literally CANNOT get insurance. That's not even factoring in the fact that I have a minor level chronic thing that I need to see a non subspecialist for a few times per year. I dont intend on getting sick, and in reality, theres really a very small likelyhood that I will ever need to be hospitalized again, but that small chance to a business executive in an office somewhere means "this guy COULD get sick, and as an insurance company, we dont want to have to help him"