Here's why:
* Clarity: Quotation marks within a speech bubble can become visually cluttered and make it harder to read.
* Convention: This is a common practice in comics, manga, and graphic novels.
However, there are a few exceptions:
* Dialogue within dialogue: If a character is quoting someone else, you might use quotation marks inside the speech bubble for clarity.
* Emphasis: Sometimes, quotation marks can be used for emphasis, such as when a character is quoting a specific phrase or term.
* Specific style choices: Some artists may choose to use quotation marks for their own stylistic reasons.
Ultimately, the choice of whether or not to use quotation marks in speech bubbles is up to the artist and the style of the work.