Because from the client downloads assets and we are more used to thinking about what happens from the client's pov. Alternatively, it could be for the same rea

Because from the client downloads assets and we are more used to thinking about what happens from the client's pov. Alternatively, it could be for the same reason people usually say they're going "up" to a big city, regardless of the direction of travel. The server is the hub and all the clients are down from it. This possibly dates back to when towns/fortifications were usually located on hills.