This naming makes sense because:
* Vowels are the sounds that are produced with the least obstruction of airflow in the mouth. They are the "open" sounds, as opposed to consonants, which require more constriction or blocking of airflow.
* Vowels are typically the sounds that carry the most prominence in a syllable. Think of the difference between "cat" and "cot." The "a" and the "o" are the sounds that give each syllable its distinct character.
So, "vowel" literally means "voice-like" because they are the core sounds of speech, carrying the most weight in syllables and requiring the least effort to produce.