Coverage for pre-existing conditions and up to 26 year old being on their parents insurances are the two things I support in the ACA.
Used to be if you had one insurance, and you wanted to switch to another, you would not be covered for the pre-existing condition for 6 months or 1 year depending on the company you were switching to. Or if you are employed somewhere and want to add your spouse on the insurance (you typically pay extra to cover spouse) if your spouse had a pre-existing condition it would not be covered for a period of time.
One of the biggest problems with health insurance is that for most people, they don’t own their policy. When they change jobs, they lose the old because it’s not theirs. A whole host of other problems arise from that.
As just one issue, constantly changing plans makes the costs more uncertain for insurance companies, and people pay for risk. People hop on with no record, no history of paying in.
They have no long-term relations with an insurance company - which became exponentially worse with the ACA being designed to cause people to be kicked off of policies, such as outlawing policies which had very good coverage, or had returns which were not between 10x +/-2% (bronze 58-62, silver 68-72, gold 78-82, or Platinum 88-92%) of medical expenses. Your plan averages a payout of 73%? No longer grandfathered, and in many cases no longer permitted. New plan.
That issue alone makes it very difficult to go back even to what was.
If you owned your health insurance policy, I’m sure insurance companies would have been offering such things as the 26-year-old thing as a rider - similar to what they do with life and car insurance.