People need to understand that the only thing in this game is the environment and vehicles, this isn't like GTA where you have 128 NPC's running around on screen/driving cars with the intense details of the city. You can't compare them.
Also let me put this logicically, you're going about 250km AN HOUR max. It'll take you absolutely hours to get from one side to the other. Sure its seamless while you drive that distance, but if you where to teleport to the other side you'd get a loading screen. 40,075.0 km around the equator and this game is 14,000 km. I have a feeling they've miss said the distance.
Let me explain why I believe this, imagine making a map for Blockland with mountains/roads/tree etc, that'd take you quite some time and you'd only have about 1km squared max. times that by 14,000. Sure they've got tools that allow them to do it faster like auto road making tools but really think about that again, that's 14,000km they've got to make sure isn't loving up, tree's going throw rocks, things floating in air. Manually flying throw the game like F8 in Blockland would be useful but still slow checking all of the area's.
But I'm definitely going to buy it, multiplayer in free roams are always fun.