You know that a cryogenic freeze has some non zero probability of success. Sure the odds are dismal today as our science and understanding of the mind is so poor - but it is not zero. If the physical structure survives, it is probably possible to eventually tear down their frozen brain and recover their stored memory and personality, and experiments conducted by MIT have attempted to do this recently with small sections of rat cortex. (and it sort of works, well enough to show the process is feasible although of course the emulated brain slice doesn’t exactly match the original because of flawed current models)
Therefore freezing patients when they first develop dementia is the rational treatment to try. Convince me otherwise.
I think the reason this is not commonly done now is because of the influence of irrational religion. If you reject religion and model expected outcomes purely by the known physical world, this is the correct action to attempt.