Please read my post #25.
Most of the majors offer both Supplement plans and Advantage plans.
So you can’t really declare that a company is enjoying explosive growth if it is not outperforming the S&P, and offers both plans.
There’s mostly no magic. You pay the big Supplement plan monthly, in comparison to $0/month Advantage, and until you get sick, that is reality and accumulates a difference. After you get sick, you pay Advantage co-pays — which have an annual max.
As for travel, both categories will provide some coverage out of your area — but frankly, if your trip is to be substantial you should have travel insurance.