why doesn't "chuối" have/need a "những" before it?
Does this sentence not say: "Monkeys eat banana"?
For nouns with one syllable, you can safely ignore the classifier. It sort of acts like a compound verb -like bird-watching. We don't know how many birds you watch, but that's what you do - bird watch. So ăn cơm = eat rice (have dinner), mặc áo = put on a shirt, etc.