So now, the appearance of Pei Xuanjing and his proposed Godsealing Plan present an opportunity they cannot refuse. Unless the Xuantian Sect is willing to give up this chance.
In the past, they might have fought to lead this plan or started from scratch.
But things are different now. Not to mention that the various immortal sects are presently on equal footing, each with a single True Immortal, none weaker than the other.
The strength that Pei Xuanjing, the Shenxiao True Monarch, has shown is so formidable that even Daoist Xuantian is wary of him. To start from scratch would be to directly oppose him in a fight to the death, something the Xuantian Sect cannot afford to do.
And with the Sword Sect and others already having agreed, the Xuantian Sect has no choice but to agree as well, unless they are willing to forego this opportunity.