Cryonics is the idea of freezing someone for a long period of time until the cause of death is curable (including general old age). This is not really the vision of immortality most people want and there was evidence presented on sci.longevity that freezing and thawing produces so much cellular damage that all you end up with is a person shaped pile of meat product. It's also a tempting target for fraud, since your customers pay in advance and don't complain.