This is a chart from the CBO score of AHCA, the House-passed bill to repeal-and-replace the ACA.
Yearly premiums for a 64-year-old making $26,500 a year would go from $1700 under ACA to *$16,100* for the same insurance.

This is basic math. If somebody is getting a subsidy accounting for ~90% of the cost, and that changes to a flat ~20% while regs protecting older people from price hikes are weakened, their premiums will skyrocket. Hard to cut >$1T from health care w/o pain.

Premiums for millions of people would have gone up, not down, if AHCA had passed. That presented a big political problem because GOP had been promising lower premiums. So a key solution: State waivers and the MacArthur Amendment.

By diluting benefits or charging sick people far more money for insurance, states could lower premiums for healthier people.

Overall, the pat of butter (subsidies) would be spread up the income scale, but the pat of butter would be smaller because of the repeal of the ACA taxes which paid for them. So, less butter to spread over more eligible people.

AHCA scored as cutting the deficit, but that was helped dramatically by the assumption that 23 million fewer people would have insurance. Gov't saves money when people drop subsidized insurance or Medicaid, etc.

You couldn't pass AHCA today under the budget rules. Why? GOP/Trump eliminated the individual mandate in the tax law, allowing them to enact additional tax cuts & make the corporate tax cut permanent.

Ending the individual mandate scored as saving the government hundreds of billions over a decade because of people dropping subsidized insurance, etc.

The replacement bills - if there are any next year - would have even less butter to spread in subsidies as a result, or have to keep/revive more taxes. (Unless CBO dramatically changes the scoring.)

Fun fact: Ask why there was money still available for subsidies at all in AHCA after they repealed the ACA taxes?

Answer: That's because AHCA kept most of the Medicare provider cuts from the ACA. (Yes, the Medicare provider cuts Paul Ryan promised to end in his VP convention speech and the NRCC has run ads against cycle after cycle).

Another interesting thing about the Medicare cuts: A lot of providers' groups backed the ACA anyway. The tradeoff for shrunken Medicare reimbursements was they were going to get ~30M new insured, paying customers.

So, was the health care fight about pre-existing conditions? That was a part of it. But tax cuts, shrinking spending on subsidies and Medicaid and ending the mandates were very big parts of it too.

The hard part in health care is how to get it so it's not so expensive in the first place. Other countries treat health care more like a utility - a required service with regulated prices. That hasn't been the USA way on health care, but it is on say, water utilities.