They knew a lot about Dusk intelligence; they knew that once Proxy Agents approached Dusk, the presence of Dusk milestones would wane. Such an environment allowed them to construct a True Illusory Realm to interfere with the Proxy Agents' judgment, causing the opposition to inadvertently deviate from their course and never reach Dusk.
Yet Zheng Yichen ignored such illusions.
The surrounding Boundary Breakers felt they were at their limit and could no longer intercept Zheng Yichen. The instructions they received were to avoid close combat with the enemy, lest they be killed and become mobile blood packs for the Proxy Agent.