The biggest amusement parks are the ones with the longest walks between attractions
This is true. But they aren't building an "Open Amusement Park", it's an Open "World", where the key is that they're emulating the foibles of the "real" world. The real world is filled with negative spaces or empty areas of which most people don't find interesting, they're just transitory spaces that connect a point to another.
Now you could argue that games are closer to amusement parks in purpose so they shouldn't be emulating the real world and should compress everything to be next to each other. There are games where natural geography causes that to happen, such as cities but other large landscapes fall flat when they're highly compressed. Skyrim in particular falls prey to Potatoland, where quest givers are practically standing next to their quest objective. I think many games find a happy medium between a sense of place and compression.
Two obvious solutions to deal with traversal of large spaces is to make traversal fast, or to make it interesting. It remains to be seen if either of those apply here, but still, we should expect Space to be empty, there is a reason it is called that.