If you are a big official, you will be very arrogant. Perhaps because of his growing status, his eyes are getting bigger and bigger, and even the emperor is not so obedient. It is said that once on the way back to Beijing, other governors knelt on the ground to meet him, sometimes even ignoring the imperial edict, which seemed a bit overbearing.
Corruption. When his official position is getting higher and higher, he will inevitably lose control of his desire for money. Therefore, Nian Gengyao did a lot of corrupt things under the emperor's nose. Nian Gengyao did all these things, such as embezzling food, embezzling taxes and embezzling people's money.
Participate in the succession to the throne. When Nian Gengyao was in office, he supported Sanmei as the heir to the throne, and Yongzheng, who had experienced "nine kings taking office", hated this kind of behavior. And I am very afraid that such a thing will happen again. If Mei becomes emperor, then Nian Gengyao will have the right to stand up. And he was domineering, and no one could control him at that time. So Yongzheng was right to get rid of him for his successor.