My guess as to why cryonics is the best method currently available is that it's the best bet for keeping you potentially alive until better methods are developed.
Speaking just for myself, I'm not convinced that any method can give immortality (Murphy happens), but there's a good bit of hope for greatly extended lifespans.
What we know about cosmic eschatology makes true immortality seem unlikely, but there's plenty of time (as it were) to develop new theories, make new discoveries, or find possible new solutions. See:
Cirkovic "Forecast for the Next Eon: Applied Cosmology and the Long-Term Fate of Intelligent Beings"
Adams "Long-term astrophysical processes"
for an excellent overview of the current best-estimate for how long a human-complexity mind might hope to survive.
Just about everything CIrkovic writes on the subject is really engaging.
What looks, at the moment, as the most feasible technology that can grant us immortality (e.g., mind uploading, cryonics)?
I posed this question to a fellow transhumanist and he argued that cryonics is the answer, but I failed to grasp his explanation. Besides, I am still struggling to learn the basics of science and transhumanism, so it would be great if you could shed some light on my question.