The planet is really big. It has a couple of characteristics which has had as a result that the planet is not yet fully explored. Travel across certain regions, like deserts and mountain ranges is simply too hazardous or expensive to be done regularly, even with the aid of modern technology and magic.
There may be civilizations of some sort in all different regions of the planet, but these civilizations will have little or no contact with each other.
The deserts around the equator are too large and too hot to allow for normal travel. Magically shielding against the heat of day and cold of night might be possible, but the cost of bringing along enough mages to support such shielding for as long as needed far exceeds the profits that might be made from doing so.
Crossing the highest mountain ranges is subject to similar restrictions. The forces of nature make passage on the surface too treacherous to be viable. Using the tunnels of different dwarf colonies might be possible in theory, but will likely be difficult in practice.