Someone makes something change. In Japanese sentence, there are (at least) SUBJECT, OBJECT and the transitive VERB.
The focus is on "someone" who does the action.
Something itself does an action. The constructure in Japanese is (at least) SUBJECT and the intransitive VERB.
The focus is on the "action" done or seems to be done by itself, or naturally done. It's not important someone who did/does even thought she/he/it exists.
Please take a look at this:
Example with TO OPEN: 開く(あく intransitive) and 開ける(あける transitive)
I open the door. 私はドアを開けます。
The door opens.ドアが開きます。
*Maybe the door opens naturally by the wind, for example, or someone opens the door but the subject isn't important in this sentence.
I hope this helps you.