In a "trade run" what you are moving around is a crafted good called a "Specialty Good". They can only be crafted in the regions they are a specialty of (and at one specific crafting station). Like, if you are crafting Canadian Bacon, you can only craft that in Canada. This is the middle ages, after all. So you craft your Canadian Bacon, or more seriously your Tigerspine Grape Jam, in Tigerspine, and carry it in some other area of the game where that is in demand. These goods are not needed by players, the demand is artificial and issued by NPCs, but if a player steals your pack they can deliver it in your place and get 80% of its value (20% goes to the original owner, as consolation).
The player economy does not only revolve around these NPC-demanded packs, but this is the mechanic that forces (for the "build token" rewards) players to move around the map at walking speed (or sailing), creating targets for emergent open PvP gameplay. At least these were the intentions. How healthy this kind of gameplay will be in a developed server is another story that I cannot predict.