People ONLY travel to the USA if there's a specific specialist they really need to see - that one clinic for that one kind of cancer nobody else seems to be good at solving.
That is REALLY niche, though, and it's only something that wealthy people can do. Overwhelmingly, though, medical tourism goes the other way. Once you've bought your air fair and accommodation, and paid the medical costs, you've still spent maybe a third at most of what your health insurance would have charged you out of pocket.
NOBODY goes to the USA to save money. They go there if they have the cash to drop on that extra special treatment, but again, that is a niche thing.