Cryonics isn't a life extension strategy, it's an immortality gambit.

You have this the wrong way around. Cryonics can only succeed in the event of practical immortality being achieved which requires that radical life extension is achieved. It's a necessary (but importantly not sufficient) condition of revival that the technology exist to radically extend lifespans in which case there will be nobody signing up for cryonics and no market to develop the technology to defrost and revive.