Here's why:
* Intransitive verbs do not take a direct object. They express a complete action without needing an object to receive the action.
* Transitive verbs require a direct object to receive the action.
In the sentence, "arrived" expresses a complete action (the act of reaching a destination). It doesn't need an object to make sense. "Early" is an adverb describing how you arrived, not an object receiving the action.