You misunderstand, likely due to the challenges of translation and of explaining one language using the words and constructions of another.
Verbs like 潰【つぶ】れる and 漬【つ】かる are not passive, but rather stative -- they describe the state of something. For 潰【つぶ】れる, the meaning is not passive "to be crushed by someone or something". Instead, it may be understood more like "to be (or come to be) in a state of crushed-ness". The emphasis is on the state. This contrasts with the active verb 潰【つぶ】す "to crush something" and its passive conjugation 潰【つぶ】される "to be crushed by someone or something".
This stative quality is like the verb 開【あ】く "to be (or come to be) in a state of open-ness", contrasting with active 開【あ】ける "to open something" and its passive conjugation 開【あ】けられる "to be opened by someone or something".
Please comment if the above does not address your question.