Actually none of them wants pearl. The Babylon leader sees the duplicated copies of certain types of lux and short supply in other type of lux. So Nebby arranged this complex trading scheme to act as a middleman. In the end, three nations will benefit from the trading scheme by increasing happiness by 4, maybe 8 for Polynesia but their people probably already trading pearl to the other continent. The trading also bonds the nations closer to achieve greater prosperity together.
Apology to Inca leader who we may help us hurry up Polynesian leader to make a quick trading decision THIS turn. Babylon people will make up to the Inca people by returning other favor in the future
Several Babylon bowmen are on the way to help conduct policing duties on our continent, given that populations start to settle into cities from countryside, and criminal activities may start to rise with dense population.