For example, it seems unlikely to me that when legislators authorize a one year prison sentence for shoplifting, they mean that a person could receive a year in a Supermax. I think legislators should have to authorize such a sentence explicitly. There might even be a claim that such statutory distinctions are required. If society begins to recognize Supermax sentences as different in kind than other custodial terms, one might argue that a legislature's failure to explicitly authorize such punishment makes such sentences unconstitutional.
This could call for due process protections in connection with this separate distinction, but, why shouldn't prison officials be able to state the facts that justify a transfer to a much harsher situation for a prisoner? It isn't as if there is not, in the vast majority of cases, a factual basis for the decision, which means a very great deal to the prisoner, supported by testimony from law enforcement personnel and other evidence that can be offered to support the decision. Even in cases brought out of the blue in the real world, well over 90% of prosecutions result in convictions.
Also, the downside for society of a government loss in a Supermax transfer decision is far smaller. When a guilty man is acquitted in an original trial, society faces the risk of a man (or conceivably a woman) who has committed a serious crime and may do so again, at large with no supervisory conditions on his (or her) activities whatsoever. When a transfer to Supermax from another prison is denied, the individual still remains incarcerated, generally for very long terms, and can still be subject to disciplinary measures within the context of the ordinary prison.