Why can the Red Army cross the Dadu River but not Shi Dakai?

Shi Dakai was flooded ahead of schedule, but there was no flood when the Red Army crossed the river. This is the right time, the right place and the right people, which is not good for Shi Dakai. In addition, the Red Army faces a divided national army. At that time, Chiang Kai-shek was not yet unified, and the warlords of all walks of life kept their strength, which not only prevented communist party from defending Chiang Kai-shek, but also prevented many local troops from dealing with it, and did not really stop the Red Army. But what Shi Dakai met was a stubborn Qing army with unified command and monolithic structure. It is several times stronger than when the Red Army crossed the river. If you change your role, you still can't get through those days. If Shi Dakai can easily get through Anshun Field now, there is no need to rush across Luding Bridge from far away. At least the Red Army didn't meet the enemy in Songlin River, but Shi Dakai met Ying Yuan, the stubborn toast, and even demolished the small iron cable bridge. Going to Luding is a problem. Moreover, there are many Qing troops on Luding Bridge, and the Red Army is in Luding. There is only one class guarding the bridge, which is simply intended to let the Red Army pass. At that time, the enemy Shi Dakai encountered was 10 times that of the Red Army. Even if Shi Dakai took a step back and went to Xikang, it would be impossible, because the Songlinhe Bridge had already been demolished, and the enemy in the west firmly besieged him in the ravine. At that time, no one could have passed his situation.