While we're speculating, I think it's that "kin work" (keeping up with family and friends, taking care of the elderly, child-rearing) primarily falls to women. Churches provide a framework to do that. If you've noticed, women are highly active in the parts of a church that aren't explicitly about God -- fundraising committees, education committees, various organizing functions. It's community-building glue.

Cryonics, unlike Mormonism, doesn't have that aspect. As of now, it's a transaction made by an individual. I'm not sure how one would make cryonics by itself "church-like."

You could try to make a rationalist social institution -- like a Masonic lodge -- that combined charitable work, socializing, activities for children, educational lectures, and activities/volunteering opportunities for the elderly. Cryonics could be built into that. The point is, it has to be a family and community institution.