1. The Qing Dynasty was already very rich during the Qianlong period.
Gan Long's grandfather and father laid the foundation for his prosperity. When the Qing Dynasty was first established, the tax system was incomplete and the national income was not much. When there is no tax system for gentry, the tax of gentry is protected by the state, because gentry is a good bridge between the government and the people. At that time, the gentry not only did not have to pay taxes themselves, but also their families did not have to pay taxes. So many gentry made a lot of fields under their own names. As a result, there are more and more such gentry, but the national tax revenue has decreased.
Therefore, Yongzheng approved the gentry's errand system, which solved this problem well and the national tax revenue gradually came up. Yongzheng also set many rules for the gentry, and this system was also very useful at that time. This country will gradually become richer. By the time of Qianlong, the country was already in a state of enriching the people and strengthening the country. There was no need to increase taxes in this way, and the gentry did not like this system, so it was abolished in light of the situation at that time.
2. Influenced by the political environment at that time
When Qianlong became emperor at the age of twenty-five, he was still relatively young. Yongzheng also left him four ministers, and Qianlong would ask them everything at first. I think it's because Qianlong's foundation as emperor is still not stable, and he needs to do something to win the hearts of officials, so he canceled the gentry's errand system and gave them some benefits.
3. It may also be related to Qianlong's personality.
Qianlong likes Kangxi's idea of ruling the world with benevolence, and will learn from Kangxi, not as strict as his father. I think it's good. Being strict with others will make people more convinced and not offensive.