If you or your dependents have any medical complications or are something other than young and healthy, the costs can increase drastically. Also employers often provide a lot of resources via HR and FAQ websites for navigating health care related topics. And I think there is safety in numbers so to speak. Insurance companies don't care at all if they loose one customer. They care a lot if they loose a big contract with a big company. Maybe they'll decide you provided false information in one of their 1,000 forms and thus will deny coverage when you desperately need it. They're less likely to pull that sort of crap if you can complain to your employer and have them apply pressure.
Put simply: there's little incentive for health insurance companies to provide good service to individuals; there's lot of incentive to provide good coverage to company employees.
If that really is the problem then you, as a freelancer, can hire a company to navigate and negotiate the health care plans for you and other freelancers as a pool and get the same quality and discounts as you would in a large corporation.
But even so, they'll be a middle-man and they'll try to take as much profit from the group discounts they get instead of passing those savings on. An employer doesn't have an incentive to make profit there.
I don't know, do they? If they do, then your premise is correct and there's enough benefit in negotiating in groups that it's worthwhile. If there aren't, then it's either a) the "economist sees a 20 on the ground and immediately assumes it's fake because someone else would have picked it up otherwise" or b) your premise is wrong and having a large HR department doesn't make a difference in your plan costs and pricing.
The real answer is that they do exist. I used Oscar for a year and their plans were actually by either United Healthcare or Aetna (I don't remember anymore) and the premiums were less and the quality was identical to what I had through a company provided insurance later. There's also Justworks that does something similar, though they're more of a full HR service provider.
Put simply: there's little incentive for health insurance companies to provide good service to individuals; there's lot of incentive to provide good coverage to company employees.