Originally Posted by
Gilraen
It's not an issue of lore or universe. It's a game mechanics issue. The game updates at a certain rate, I think I heard 0.2 seconds? Mounts move at a speed that translates rather easily to this rate. But, the faster you go, the more you start to outpace the game so much that enemies around you don't immediately spawn in. This could be pretty bad if you're in the new Heavensward areas. This is why ground mounts only move so fast and mounts that are flying don't aggro unless really low to the ground. For a more extreme example of the speed issue you should try flying around in Minecraft in Creative mode. Eventually you'll find yourself moving faster than the game can populate chunks.