The reason was to fulfill the promise that Miao Yi had made to the School of Blue Jade.
From Yan Xiu’s perspective, Miao Yi’s method of solving problems would generally start with provocation. Once the situation had been instigated, Miao Yi’s involvement would come next. For example, when he first came to East Arrival Cave to assume his position, the first thing he did as a Cave Master was to secretly destroy the mountain gate. Afterwards, he would proceed with his murderous scheme by blaming someone else.
No matter how he looked at it, Yan Xiu could only see the present situation as Miao Yi’s intentional provocation. Otherwise, based on Miao Yi’s aptitude to lose his temper and then start a war, there was no way that he’d have the patience to watch those people leisurely arguing with one another.