I think the real reason people are reluctant to sign up for cryonics is that it raises all the classic red flags for a scam. People are asked to invest a significant amount of money in a non-mainstream plan that, even if it works exactly as claimed, won't pay off until well after the mark is no longer able to sue.

Consider the situation from the perspective of someone just hearing about cryonics for the first time: if cryonics is a sham, then they should expect to be presented with a lot of generally plausible-sounding (but falsified) evidence, most of which will probably be too technical for them to follow (so that they can't figure out that it's bogus).