Here's why:
* The show is generally G-rated. This means they try to avoid language that might be considered too mature for young audiences.
* Rainbow Dash is known for her energetic and somewhat rebellious personality. She might use slang or exclamations, but they usually wouldn't include phrases considered too strong.
* The show doesn't have a full transcript, and fan-made transcripts might not capture every detail. It's possible she used similar phrases, like "Oh my stars!" or "Oh boy!"
While we can't be 100% certain, it's unlikely that Rainbow Dash would have used the phrase "Oh my gosh" in the show. The show's creators likely preferred to stick to language that aligned with its overall rating.