Here's why:
* Short vowel sounds are typically associated with a single vowel letter and a short, quick sound. In "love," the "o" makes a short "uh" sound, similar to the "o" in "cup" or "hot".
* Long vowel sounds are usually indicated by a vowel followed by a silent "e" or a vowel digraph (two vowels together). "Love" doesn't have these features.
So, the vowel sound in "love" is short.