But you have cardinal directions on a 2D Cartesian plane (a square), which is essentially how the game world is designed. They aren't using a polar coordinate system, which is what we use in real life. Most games actually design worlds like that since it is easier to imagine the field as a huge square than as a sphere with poles. Unless you are using complex engines, it's very hard to actually create poles in a 3D space for MMOs. The only game I can think of from the top of my head that is actually going to do that is Star Citizen, cause I know Elite Dangerous does create absolute cardinal directions, for the reason I said. They tried using polar cardinal directions, but it was essentially overloading the servers. Now the reason why you can't just change the cardinals direction to be just a set of arrows on the side is because when you walk on a Cartesian plane, the cardinal directions are not relative to the observer. Sets of arrows would make the cardinal directions relative, meaning no matter where you look you are looking in the north direction. Which then would make the entire planetary axis relative, which would mean that me giving the coordinates (1,0,2) could be the exact same as you giving (100,0,-45). Since the axis is dependent on where you are looking because the cardinal directions are fixed arrows relative to you, not the world. I had a professor that taught game coordinate mathematics once, really interesting stuff. Everything here was his take on it, there are a number of ways of looking at the situation and extrapolating your own rules, since after all you are the creator of the universe and can create your own rules, there are games where direction is 100% relative to the observer (player) and the only way to really coordinate meeting is by using landmarks.
Also if you really think about it, even on Earth you could argue that in a small scale the world functions more as a 2D Cartesian absolute system than as a 3D polar system. Since the only way to really notice changes on a compass would be by traversing immense distances. For example, walking from 1 end of the US to the other you would have a noticeable change, however going from east to west New York city you wont. It's why when crossing long distances in planes you notice the flight path is parabolic, not linear. Because the parabolic arc essentially negates the fact there is a pole(turning it into a 2D absolute pole system), while a linear path would not take into account the poles and you would miss your destination.