Here's why:
* Short vowel sounds are typically found in words where the vowel is followed by one consonant. In "baby", the vowel "a" is followed by the consonant "b".
* Long vowel sounds are often found in words where the vowel is followed by a consonant and a silent "e" at the end of the word, or where the vowel is followed by two consonants. This is not the case in "baby".
The "a" in "baby" makes a short, quick sound similar to the "a" in "cat" or "bat".