If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
why the same thing doesn't happen with religions that believe in an afterlife
Because with religion you return to life in afterlife which is entirely different from "normal" life. And with cryonics you return to life still in normal life, just after some time has passed.
For some value of “normal”... Watch Good Bye, Lenin! -- and that was only a few months. Or see this post, and the post it's a followup to, and the posts that one is in turn a followup to.