There's probably an absurdity bias going on in the rejection of cryonics (the dead just don't come back, and frozen people look dead). It also violates tradition (burying and incineration). And in our culture, the mere image of frozen bodies in a fridge has more disgusting connotations than happy ones.

So that's my speculation about why someone who never actually thought about cryonics might reject it. Maybe if we tell those people about these reasons, they could change their mind?