Someone hasn't read their policy for "lifetime maximums." Every plan in the US has a lifetime maximums clause. Most is set around $1M, if you have really good insurance, it can be higher.
What that means is, if you have a catastrophic medical condition and your insurance has paid out $1M total, it stops paying EVERYTHING. You essentially get booted off the insurance and you are now uninsurable.
As you can imagine, in the US health care system, incurring $1M over the course of a serious health issues is not necessarily hard to do. In the five years I worked in benefits for a large Corporation, I had to boot off 6 people for hitting their lifetime maximums. (About 2500 total employees).
So even if you pay your deductibles and premiums and you have a serious medical condition, you can find yourself with no insurance and no way to get any insurance.
There's a reason that healthcare is a huge stress for a lot of people in the US and it 100% SHOULDN'T be.