Here's why:
* Short vowel sounds are typically pronounced quickly and are often followed by a consonant. The vowel sound in "woke" is the short "o" sound, like the "o" in "hot" or "box."
* Long vowel sounds are typically pronounced longer and are often followed by a silent "e" at the end of the word or a vowel digraph (two vowels together).
Since "woke" does not have a silent "e" at the end or a vowel digraph, the "o" sound is a short vowel sound.