Part of the deal is that they're procedures are based on the idea that we haven't yet developed the technology to revive someone yet ... we're sort of betting on someone figuring it out in the future. The freezing process is designed to cause as little damage as possible so that whenever someone does figure it out, the original tissue will be held in stasis with minimal damage. There is also the idea that the person would have been dying of something in the first place, so even after they get the unfreezing part down, they still have to wait around until the cure for whatever killed you in the first place is available.