The trap had to appear rational and justified for the opponent to fall for it, and in the eyes of others, Zheng Yichen's current actions were motivated by ample reason.
If he was too close to the City of Dawn Light, the summoning ritual process could be discovered. However, a few small "accidents" during the process led to Zheng Yichen's activities being "exposed" prematurely.
As a result, he became surrounded. More importantly, he wasn't a "demigod" known to the demigods who arrived; only a few of them recognized him.
This gave them a reason to attack, for while a demigod might not always be greedy, when the time came to show greed, they didn't need to hide it. As demigods, they were part of the world's upper echelon of power. Without the true gods entering the fray, demigods were essentially the strongest combatants.
