Here's why:
* Short vowel sounds are typically quick and sharp, like the sound of "u" in "cup" or "i" in "bit".
* Long vowel sounds are typically drawn out, often sounding like the letter's name, like the sound of "a" in "cake" or "e" in "tree".
The "u" in "suit" has a short, clipped sound similar to the "u" in "put" or "nut".