I don't think this is in spite of subsidies but beacuse of them. Just like the epipen mess, the less of a bill the customer sees the more you can raise it.
Outside of health care specifically, this is also why disability plans tend to be relatively inexpensive for large companies to offer but are pretty pricey--when you can even get them--for individuals.
Same with disability, examine the individual coming in to make sure they don't already have a disability that's being covered, but after that why would the individual odds be any different than accepting a whole group? If you do an actual exam, they might actually be better.
There are non-employer group plans for certain types of insurance e.g. through something like the IEEE but generally not for healthcare AFAIK.
With respect to disability--leaving aside that an exam won't find all pre-existing conditions such as joint problems--there's still adverse selection. The people who would even apply for disability insurance are a higher risk pool (probably older for one thing) than the working population as a whole or all employees working at a large company.
Those who work for a company and receive a W-2 form can look at Box 12 on the W-2 to see how much their employers paid for their side of their health insurance policy (coded with "dd").
You might think "who cares" but that's money that could have gone towards your salary.