That could be because they believe that everyone will be resurrected.

Assuming your closure hypothesis is true, I think this is it. With cryonics, not only do you have to worry about the low chance of getting resurrected, but you also have to worry about the state of the cryonics facilities that store your loved ones while you're still alive.

I doubt this is the case. Were this the case, wouldn't the solution be obvious? Why are they objecting to cryonics, rather than also signing up themselves, if they agree that cryonics is plausible and fear their loved one being resurrected and them not?