Well, you said you are dumb and figured it out... I'm thinking the reason this game makes any sense to you is specifically that you are dumb and the game is dumb. This game makes no fucking sense. There is no logic in how any of it works. Only someone not using logic would think any of that is a good idea.
Think about it. Slaver role gives you a bonus to selling slaves. There is no option to sell slaves. That should immediately tell you it's a horrifically designed game.