Bear in mind that my map making experience is limited from the dark ages of terraformer.exe, to FP’s Visitor, ArmA’s Visitor2, ArmA2’s Visitor… To whatever they call it now. Anyways, same general rules tend to apply, whether it’s Unreal, BoX, or DCS:
There’s typically a scale set by the engine. In the case of Unreal, your maps have a limited size/resolution, so if you want a certain level of detail, your scaling has to take that into account. What that means is if you want to have a high detailed map, with fine terrain tiles, your overall play area is highly restricted. If you bring the scales down, you can get a larger play area, but you sacrifice terrain detail to get it.
Ergo, for an engine like what powers FP/ArmA, your max resolution is a height map of 4096x4096. Your satellite image can be several times this size, so you can make up for some height map limitations by painting features on your sat map. Depending on the engine, there’s also a low/close in map which is used to place higher detailed texture tiles when within a certain view distance. I don’t know if DCS or BoX use this kind of system or not as it’d be wasteful for a flight sim, so if I had to guess they stick with a pure sat map for detail, likely cutting out chunks of it and displaying chunks as required from what I’ve observed.
In theory, if one was willing to accept a bit less detail, you could make a map twice the size, but half the resolution. That would mean less defined terrain features, more angular/blocky looking mountains, and so on. IMO I’d be willing to accept this if we had a bit more in the way of strategic aircraft as well as gameplay, but thus far we’re pretty much in the camp of tactical. We also have limitations with regards to how objects would be interacting over such large distances, which is troublesome for an engine like Unreal. FP/ArmA handled it by reducing how often units outside of the player(s) view were updated, but a flight sim is a bit more prickly about that, especially when you have assets like AWACS that can see a lot. This also places a lot of demands on servers as they have to keep track of objects interacting with all the players.
Basically, you end up with a kind of distributed computing problem as your map size grows. You have a detail limit that’s based on overall computing power (which is also used for complex stuff like fluid dynamics on your flight models and those are highly intensive), then you have further monkey wrenches that all vie for that same power. So you have to balance an acceptable level of detail to fit what the goal is; a flight sim has to compromise a lot here in order to be, y’know, a sim. Fortnite? PUBG? CS:GO? They don’t have nearly the same demands or problems. Basic physics, handled at the client level, uniform for everyone. 100 players? Please. Thousands of AI controlled units are a much bigger problem.