Bridges and Highways facilitate travel, thus reducing costs, as Donald X has said. The Bridge Troll has presumably been hired to your services, and is able to collect tolls from foreigners to make goods cheaper for your people. The Princess has suitors begging for her hand in marriage, and in order to be seen as most attractive, sign treaties with you, her non-gender-specified royal parent, removing tariffs on goods from their kingdoms, making them cheaper. Much cheaper.
Why, literally, do Haunted Woods make you keep useless cards in your hand from turn to turn?