That isn’t insurance. You don’t need low-risk people in the pool for insurance to work. Insurance premiums are technically derived from individual risk, not the risk of an arbitrary pool. Pooling is only done to reduce the tail risk of the underwriter, it doesn’t materially change individual premiums.

You do need low-risk people in the pool if you want low-risk people to subsidize the insurance premiums of high-risk people. That is not insurance, that is just socializing the premiums of high-risk individuals. These distinctions matter when discussing policy. Socializing medical costs may be the appropriate policy choice but lets not smuggle it in by abusing a term of art like “insurance” which means something very different.