Here's why:
* The vowel sound in "have" is a short "a" sound. This is the same sound as in "cat", "hat", and "man".
* Long vowel sounds are typically represented by a vowel followed by a silent "e" or a double vowel. Examples of long vowels include "ate", "bee", "see", and "tree".
So, the vowel sound in "have" is short, not long.