Humans are wired to respond to immediate death threats very effectively. When you're overtaking a truck on the freeway and it starts to pull out into your lane, you do whatever it takes to save yourself without thinking about it.
On the other hand we do not perceive longterm risk very effectively. This is why millions of people still smoke cigarettes. It took a long time even to persuade people that seat belts were a good idea.
That said, I am not sure that selling cryonics on the basis of alleviating fear of death is really a good strategy anyway. I think many people could be acutely afraid of death and still show little interest in cryonics. Most terminal patients, for instance.