My survival instincts prevent me from committing suicide, but they don't tell me anything about cryonics.

Well, your instincts evolved primarily to handle direct, immediate threats to your life. You could say the same thing about smoking cigarettes (or any other health risk): "My survival instincts prevent me from committing suicide, but they don't tell me anything about whether to smoke or not."

But your instincts respond to your beliefs about the world. If you know the health risks of smoking, you can use that to trigger your survival instincts, perhaps with the emotional aid of photos or testimony from those with lung cancer. The same is true for cryonics: once you know enough, not signing up for cryonics is another thing that shortens your life, a "slow suicide".