My first sentence was an (maybe not so) obvious joke.
No, this makes the scenario even more unrealistic, because approximity to home-turf would mean that the Nilfgardian army was able to resupply and recover in short time.
How many days are you spending in the game? Does anything really change in the game-world? No!
10000 people is a big city by medieval standards. My point is, an army of this size occupies a far bigger area than the fort no matter how much you quote the lore.
Accross 50 square miles much smaller armies would engage in some form - or you could at least witness Nilgardians fighting Drowners, wolves or bandits. Please, stop defending this obvious flaw in the game. All events in W3 are displayed through triggers namely starting quests and dialogues - the world itself is not dynamic! I haven't seen one supply convoy in 100 hours.