Here's why:
* Short vowel sounds are typically found in words with one syllable and are often followed by a consonant. Think of words like "cat", "dog", "sun", etc.
* Long vowel sounds can occur in words with one or multiple syllables and are usually found in words that have a vowel followed by a consonant and a silent "e" at the end, like "bike", "hope", "cute", etc.
Since "suit" has a long "u" sound, it's not a short vowel word.