what are transitive verb? and why the sentences without transitive verb cannot be changed to passive voice?
Follow the mentioned link to know more about transitive and intransitive verbs:
In passive voice, only transitive verbs are used as the object of the verb in active voice becomes the subject of the passive form. So, transitive verb has a positive relationship with passive voice.
Intransitive verb has no object so it cannot be used in the passive voice. Therefore, intransitive verb has a negative relationship with passive voice.