Basically this. Since the captaincy was decided democratically, you don’t want to get people hurt or killed - your own or the ship you’re boarding. So what do you do? Act terrifying as hell, and make literally everyone you interact with THINK you’re going to butcher them into tiny pieces. It helps when you’re at least six inches, and more likely a foot taller than most any other sailor (Blackbeard was over 6 feet, most seamen were under 5’8 because of a variety of factors).