A big problem with games in general (be it Ultimate General or WoT) is the limitation and influence that maps impart on gameplay.
Yes, the "safe flank" problem.
We tried to address this in Steel Beasts by duplicating the map in every direction, and the ability of mission designers to place units outside of map boundaries. That way you have, at least in principle, the means as a mission designer to put the player into a bigger context and to create threats on all flanks that may not actively attack him, but at least will take shots of opportunity if the player decides to always skirt the map edges.
Likewise, we added penalty zones that can be adjusted for the type of penalty ranging from very mild to severe, and how quickly they will be applied for venturing out of the designated battle area.
The fundamental problem is of course that terrain is either generated procedurally, or from geoinformation systems. The latter requires access to digital terrain databases and the tools to convert the data into your proprietary format that is tailored to deliver optimal performance. Typically these maps look less impressive (but can be huge). Or you have hand-made maps that come with a potentially very high level of detail, but since they are generated by human designers you have a direct relation between map size and the costs to generate such a map (which is quadratic, unfortunately).
So, in game design you tend to keep the map as small as can be justified, but what some game developers fail to appreciate is that the map size has a direct implication on your game design and the way how people will play it. Where the awareness exists (no doubt, wargame designers are very well aware of the issue) the question then is one of trade-offs. Do you want complete freedom of maneuver? Then you need to scale back the size of the force that the player is supposed to control, until it can realistically cover only a ninth of the mapped area. But most players like it big, so as you scale up the size of the formation/tactical level you want to hand over to the player (while keeping the maps as large as you can afford), you inevitably shrink the freedom of maneuver once that your force occupies more than the center square.
At the end of the day this is as much a question of what type of game you want to design vs what type of game you can afford to develop. Commercial considerations drive design decisions at least as much as artistic vision.