Here's why:
* Short vowel sounds are typically quick and sharp. They are often spelled with a single vowel letter.
* Long vowel sounds are typically drawn out and can be spelled with a single vowel followed by a consonant or a vowel digraph (two vowels together).
The vowel sound in "bell" is a short "e" sound, which is represented by the single letter "e" in the word.
This is in contrast to words like "be" or "bee", where the vowel sound is a long "e" sound.