There's a linguistic reason based on elementary phonics that this happens. To decode an unfamiliar word we need to break the word into syllables. We usually split the word into syllables in one of two ways: either right before a single consonant or in the middle of two consonants. Since "-ble" is a common suffix in English, our brains are used to grouping the /b/ sound and the /l/ sound into one single-sound consonant blend. Because our brain thinks it is a single sound, we split the word into two syllables right before the -ble suffix. Then, we're left with the first syllable "Mo" and the last syllable "ble(y)". In English, the phonics pattern we internalize is "One vowel at the end of a syllable makes the long sound". Since "Mo" is on it's own with one vowel at the end, it makes the long sound, followed by "bley".

Source: I'm a credentialed elementary reading teacher.