Here's why:
* Transitive verbs require a direct object. They "do something to" something else. For example: "The dog chased the ball." (The verb "chased" is transitive because it acts upon the direct object "ball".)
* Intransitive verbs do not take a direct object. They simply express an action or state of being. For example: "The sun set." (The verb "set" is intransitive because it doesn't act upon anything else.)
You can't directly "die" something. You can only "die".