Why aren't Jianghan and Tao Huang in the sixth and second groups of major crimes?

It may be no stranger to the audience that a group of people have changed and always use the same group of actors.

In addition, in the second group of the sixth group of major crimes, not only Jianghan and Tao Huang were replaced, but also Da Zeng and Bai Ling were replaced.

Yang Zhen was replaced by Da Zeng (all captains), Ding Jian by Jianghan (all veterans), Chang Baole by Tao Huang (all promising young people) and Tian Rui by Bai Ling (all female college students who just graduated and were assigned to the police station). The only thing that hasn't changed is the old Zheng He and Ji Jie. Judging from the actor's mode of play, it has not changed at all.

Again, maybe the director changed a group of actors in order to give the audience a brand-new look. Besides, maybe those actors in the first film have other jobs? But this seems unlikely, because they are not very famous and popular actors, and the film contract should not be very busy, so I think this should still be the first point I said at the beginning.