Xing Tian could not see through Haotian's plot, but Mother Earth saw it clearly. In fact, she had known ever since Haotian had started scheming against Xing Tian, but she did not speak out to stop him; instead, she tacitly allowed events to unfold.
Haotian plotted against Xing Tian, wishing to use Xing Tian's axe, which was transformed from a fragment of the Pangu Axe, to cleave his own obstinate stone body, whereas Mother Earth harbored no plans to scheme against Haotian and wished to use his assistance to help Xing Tian break through.
Even with the Pangu Axe in hand, Xing Tian, who was only at the Great Complete Stage of the Quasi-Saint, couldn't split Haotian's obstinate stone body.