Here's why:
* R-controlled vowels occur when the letter "r" follows a vowel in the same syllable. This "r" changes the sound of the vowel. Examples include "car," "bird," and "fur."
* In "liter," the "r" is not followed by a vowel in the same syllable. The "r" is at the end of the word, creating a separate syllable.
The vowel sound in "liter" is a short "i" sound, as in "bit" or "sit." It's not influenced by the "r" at the end of the word.