Here's why:
* Spelling: The vowel "a" is followed by a single consonant ("g") and then a silent "e" at the end of the word. This pattern usually indicates a short vowel sound.
* Pronunciation: The "a" in "bag" is not pronounced as a long "a" sound (like in "bake" or "face"). It's a short, quick sound.
In contrast, words like "bake" or "face" have a long "a" sound, which is represented by a different spelling pattern.