Because unlike humans, gorillas vie for mates before copulation, so they don't need big "equipment." Humans, on the other hand, engage in sperm competition so they need more of it, as well as a coronal ridge on the penis that can displace the semen of genetic competitors because *spoiler alert humans have only pretended to be monogamous maters for less than 10k years. They don't fight for mates by being the strongest or the richest (that's just patriarchy).

I know you know all of this but since you were constrained by so few words, I thought I'd add it in for good measure. 🐒😄