Hanzo wanted two because he has a habit of making dragon noodle “rafts” to chill around in. Whereas Genji uses his more as a comfort tool, Hanzo uses his more to become a floating lazy noodle dragon king.
….although it is clear the fact Hanzo has two does ruffle Genji’s fins quiet a bit and although he hasn’t asked for another one, he is clearly #not impressed with Hanzo.