Because, knowing Hillary, she'd try to do something cute to contain costs (i.e. push them to the insurance carriers) by "redlining" "pre-existing conditions" and putting those costs to the old carrier under some sort of transitional-period gobbledygook of the sort you'd expect from America's smartest woman lawyer.
However, the wealthy are among the most notorious non-payers for health care services. The widespread folk belief that you shouldn't have to pay for this service is not confined to the poor, or to RATs (just read these threads on FR!).
The poor, however, are not used to getting what they want, and so a few shekels can usually be squeezed out of them.
The very wealthy who are uninsured just don't pay, and they have reasonable lines of defense to keep hospitals' feeble (and doctors even more feeble) collection efforts at bay.