Why did Feng Yuxiang and Yan Xishan jointly fail?

The strength is not as good as Chiang Kai-shek. On behalf of the Central Committee, Chiang Kai-shek said that Zhang Xueliang's support in some places has been on the sidelines since the stalemate. Zhang Xueliang led a hundred thousand troops to help Chiang Kai-shek!

Many of Chiang Kai-shek's officers have studied in Huangpu Military Academy, and the quality of soldiers is better than that of warlords in other places.