In real life pirate days, when true pirates had been on the seas and got their hands on a sizeable amount of money, they would go to a "pirate town" where they would spend a lot on a variety of luxuries and services. Including gambling.
Treasure in Sea of Thieves feels like it has little value to it. As it only contributes to stats and cosmetics. A pirate town in Sea of Thieves would be a social hub to spend your money in. Food, drinks, boxing matches, strength duels, raggedy casinos, all sorts of things.
Edit: I honestly find it very hard to take these thread-responses seriously when people don't seem to understand what is being proposed.
In hopes to be better understood, I will add context in form of a short story: Imagine you sail to smugglers den and in the middle you see a misty cave entrance with "PIRATE TOWN AHAID" marked on a sign next to it and a guard. The guard won't let you enter without enough rep. But you have it. You enter. As you move through the dimly lit tunnel going downwards, you begin to hear faint upbeat music. As you get deeper, the tunnel begins to slowly open and you see a light coming from around the corner. The music is louder now. You can hear it echo. You get past the corner and find yourself looking at a giant cave, filled with lights and bustling pirate action. You see a bar- maybe even other players interacting with each other and drinking grog. But it doesn't feel crammed. And it feels bigger than any tavern you've been in. There's a bartender who offers different drinks. A band is playing pirate music. Now for what makes the place stand out. You see a little boxing ring you can interact with and fight in for prizes. A booth where there is a cannon-aiming minigame you can play for prizes, but you need to spend money to play it. A leaderboard. Another booth with a man that has three cups and wants you to guess which one has the ball. Where if you choose the right cup you get a prize. There is darts. You can play for yourself or with friends. There's a rock throwing game where closest rock to the circle wins. And many more things to do for fun.
The potential for actually interesting activities is only limited by our imagination. But the point being that you need to spend money to do these things. Its not free. Giving something else to spend this money on, in a social arena.
Also, its a cave for illustrative purposes. It can just as well be its own island with a town in the middle and guards protecting people from PvP - like in rust towns.
Edit: Nevermind, this is like pitching the idea of why taxes are good to a bunch of kids born in a jungle.
