Here's why:
* The "e" in "syllable" is in the first syllable, "syl-". This "e" is part of a long vowel sound, like the "e" in "see".
* The short "e" sound is usually represented by the letter "e" when it is followed by a consonant and then another consonant. For example, "bed", "pen", "set".
Therefore, the word "syllable" does not have a short "e" sound.