Why does a author use 3rd person point of view?

It allows the writer to act as an omniscient narrator. Information can be given to the reader about any character's thoughts, opinions, or feelings.

The primary advantage to writing fiction in the third person (using the pronouns he, she, they, etc.) is it allows the writer to act as an omniscient narrator. Information can be given to the reader about every character and situation, whether or not the individual characters know anything about it.