@darkdragon7341
Yeah so, there are 4 roles for the galleon: helm, cannon, bilge, and flex. By adding a fifth person to the galleon, you increase it's chances against other ships significantly, as the additional person would make galleons overpowered. You'd be able to have 2 board other ships without any loss of firepower or repairs. The imbalance wouldn't be fair to other players in this game.
The number of players each ship accommodates is balanced for fairness against other ships. They're not going to disrupt that balance to accommodate your friend group. Next week we'll probably have someone asking for 6 players on a galleon.
With custom servers in season 20, you'll have no problems having everyone on your ship on your own server, so you're sure to have a lot of fun!