I don't think cryonics organisations promise that you will eventually be revived. They promise to try, and they probably think there's a higher chance of it happening than most people do. (But perhaps not higher than most people who pay for cryonics.)
With that in mind, the structure you describe is "pay someone to try to do something that might not work", which also describes investing in startups and any number of other things.
Your objection here is that you don't think cryonics will work. That's a reasonable objection, but the way you're framing it is uncharitable.
With religion I can be quite sure it won't be a reality, as there is no trace of actual gods anywhere I look, but a lot of good evidence of it being just a social and cultural phenomenon.
Cryonics depends on the adequacy to preserve neural information of the currently used methods, of which I am uncertain but at least is in the realm of actual science.