Huo Ying's bijuu is immortal, so it is used in war by human beings.
Huo Ying's bijuu originated in Ootutuki Hagoromo, and Ootutuki Hagoromo divided ten tails into nine different bijuu. Every bijuu is an entity condensed by chakra, so according to Huo Ying's setting, bijuu can't be completely killed. Even if bijuu dies temporarily, he can reunite after a period of time.
In this way, members of Muye Village who know the characteristics of bijuu will not want to completely destroy Kyubi no Youko, and there is no way to completely destroy Kyubi no Youko. Because the essence of Kyubi no Youko is chakra, and chakra has always been a substance in the main world of Huo Ying. The purpose of planting sacred trees on the earth at night was to absorb the energy and material in the Huo Ying world, so bijuu is not a living body in the ordinary sense, and conventional methods can't kill Kyubi no Youko.
Kyubi no Youko is one of the chakra congeals formed after Ootutuki Hagoromo separated from ten tail. The ordinary means of Naruto can't completely destroy Kyubi no Youko. As long as chakra exists in Naruto's world, Kyubi no Youko can be resurrected indefinitely.
In order to protect Naruto and leave a strategic deterrent force for Muye Village, four generations of Huo Ying sealed Kyubi no Youko in Naruto. At the same time, Naruto is more suitable as a pillar force because of his whirlpool blood.
As for why four generations of Huo Ying sealed Kyubi no Youko in Naruto, I personally think there are several reasons:
(1) Naruto, who is descended from the whirlpool clan, is suitable for sealing bijuu: the existence composition that can become the pillar force of Huo Ying is quite special. Naruto also inherited his mother Uzumaki Kushina's physique. Because of its large quantity and long life, chakra is very suitable as a container for bijuu. Moreover, in the plot, Kyubi no Youko's column strength in Muye Village has the lineage of whirlpool clan, and Naruto is no exception.
(2) Watergate reserved a strategic deterrent force for Muye Village to maintain the balance of power among Ninja villages, namely Kyubi no Youko Naruto Uzumaki.
Since the development of a method that can successfully seal bijuu in the human body and use its powerful power, each Ninja Village has tried its best to keep or own multiple bijuu. After all, bijuu has unique advantages in terms of damage effect, damage range and fighting durability. Therefore, Kyubi no Youko, the water keeper, is sealed in Naruto's body, which can be said to reserve the strategic deterrent ability for Muye Village. Because of the existence of Kyubi no Youko, even though the overall strength of Muye Village has been declining, other villages dare not invade Muye Village easily. After all, Kyubi no Youko is the strongest bijuu.
(3) Watergate Seal Kyubi no Youko is in Naruto's body to prevent someone from bullying Naruto after Watergate's death, and also to lay a solid foundation for Naruto's future growth.
Watergate is quite famous in the ninja world, mainly in the ninja wars. As the saying goes, people are afraid of being famous and pigs are afraid of being strong, and Watergate has many enemies. Therefore, Watergate chose Naruto as the pillar force of Kyubi no Youko. On the one hand, it retains strategic deterrence for existence, on the other hand, it binds Naruto's safety with the collective interests of the village. Someone once called Naruto's attention to Muye Village, because Naruto was the first person to refuse, so that Naruto could survive in Muye Village even if his parents died, because Kyubi no Youko in Naruto was of great value to Muye Village. At the same time, it has laid a solid foundation for Naruto's future development, that is, compared with Naruto in chakra before Ye Hui appeared, the protagonist's aura has never lost.
Finally, to sum up, I personally think that the reason for not killing Kyubi no Youko is that, by definition, Kyubi no Youko is immortal. As for why Kyubi no Youko was sealed in Naruto's body, the reason is simple. On the one hand, it reserves the strategic output power for Konoha Village, on the other hand, it links the safety of Naruto with the overall interests of Konoha, and at the same time enhances the development potential of Naruto. Please forgive me if the analysis is not in place. If you have any other ideas, please leave a message to discuss.