Here's why:
* They are words, not direct quotes: Onomatopoeia are considered actual words in the English language, unlike a spoken phrase or a person's exact words, which would require quotation marks.
* They represent the sound itself: The purpose of onomatopoeia is to evoke the sound, not to directly quote it. Putting them in quotes would make them seem like someone is speaking or thinking that word.
Examples:
* Correct: The dog barked "woof!"
* Incorrect: The dog barked "woof".
Exceptions:
* Emphasis: Sometimes, writers might use quotation marks to emphasize the sound or to show a specific instance of a sound, like in dialogue. For example: "The clock ticked 'tock' and then stopped."
* Stylistic choice: An author might use quotation marks for onomatopoeia as a stylistic choice, but it's not a common practice.
In general, it's safe to assume that onomatopoeia should not be enclosed in quotation marks unless there is a specific literary or stylistic reason to do so.