Open world games advertise their size in square kilometres, yet a larger map does not reliably produce a larger game. Space is the cheapest thing in the production and the hardest thing to fill.
Terrain is cheap and content is not
Generating hills, coastline and forest is largely a tooling problem, and modern tools produce convincing terrain quickly.
What costs money is everything placed on that terrain by a person: a building with an interior, a conversation, a scripted encounter.
Doubling the map costs a fraction of what doubling the handmade content costs, which is why the two rarely grow together.
Every location needs a reason to be visited
A point on a map only becomes content when the player has a motive to travel there and something happens on arrival.
Supplying that motive for hundreds of locations is a design problem that scales badly. Each one needs a hook, a reward and a reason not to feel like the last one.
When the reasons run out, the map fills with collectibles and repeated camps, which is the visible symptom of space outrunning content.
Systems are used to cover the gap
Studios bridge the shortfall with systems that generate activity: wandering enemies, dynamic weather, roaming events, radiant quests assembled from templates.
These are genuinely useful, because they make the space feel inhabited between the handmade moments.
They also have a short half-life. Players recognise the templates within a few hours, and recognition converts variety into routine.
Travel time is a cost charged to the player
Distance between locations is time the player spends not playing the interesting part of the game.
Fast travel is the standard fix, but every fast travel point is an admission that the space between two places was not worth crossing.
The alternative is making traversal itself enjoyable, through movement systems or a world that rewards looking around, and that is expensive to design well.
Density is where the argument settled
The trend has moved towards smaller maps with more packed into them, because density is what players actually respond to.
A compact world where every building can be entered reads as more generous than a vast one where most cannot.
Size remains a marketing number because it is easy to state and easy to compare, which is precisely why it is a poor guide to how much game is there.