At some level, the reward-to-risk ratio is too low.
(edit:
I found a speech by Stephen Hawking on the matter:
https://www.hawking.org.uk/in-words/speeches/speech-1
Quick summary: At the start of the speech he refutes a claim that death panels exist in the UK NHS and that they would have let him die. Of course the strongest refutation is the fact that he was at the time -in fact- quite alive; thanks to the NHS.
)
Itβs not disputed nor unknown that a variety of expensive/newer cancer treatments are not payed for by the NHS. I posted one example but there are many
The difference is, that insurance costs a fraction of what it costs in the USA because the basics are all covered and the cost of providing state of the art care is drastically reduced since the hospital facilities/bed are still covered publicly.
They don't actually exist anywhere (else) afaik.