Remember the semantic restriction on ga-desideratives in (7), repeated with slight modification as (15), and then compare them with their passive counterparts with gar(u) shown in (16): 6 As (16) suggests, passivization of the whole verbalized desiderative predicate is possible only when the non-passivized plain desiderative can take a nominative object.
gadesiderative predicates but not wo-desiderative predicates are passivizable.