Xie Xun could not station tens of thousands of troops outside the city. For one, such a large force camped outside would destabilize military morale. For another, if civil unrest erupted and anything happened within the city, all casualties would be attributed to the Ningzhou Iron Cavalry. If they seized this opportunity to cause trouble, the Twelve States would be thoroughly split into two factions, completely fractured.
Xie Xun could not retreat to Ningzhou either. If he returned to Ningzhou, the Twelve States would become even more emboldened, following the example set by Lin Zhi's actions in the state mansions of the Twelve States. If they did not want to betray the court but also did not want the Ningzhou Iron Cavalry to occupy their cities, the best course of action would be to sacrifice themselves for integrity. Xie Xun could not step over Lin Zhi's corpse to seize Jiaozhou.