I don't think the fire metaphor is right exactly because encryption is reversible as you say. A better metaphor would be hiding information and only you knowing

I don't think the fire metaphor is right exactly because encryption is reversible as you say. A better metaphor would be hiding information and only you knowing its location. Knowing a password to decrypt information is functionally similar to a situation in which you have hidden documents and only you know where. In the case of hidden documents, warrants/subpoenas are used to compel their production. Certain actions (like holding someone in contempt) can also make cooperation more likely (though not guaranteed). Why do similar procedures not suffice for encryption?