First of all, if you want to reincarnate, you must meet three conditions. A reincarnated person must have a previously used body, a sacrifice and a soul, all of which are indispensable. When I first took the test, there was such a fragment. At that time, orochimaru reincarnated the previous generations of Huo Ying to deal with three generations. Although three generations of Huo Yingyi were at a disadvantage at first, he was not easy to bully. He directly summoned a god of death and gave all the hands of the first generation, the second generation and orochimaru to the god of death. Before the seal was lifted, these generations of Huo Ying people lacked souls and naturally could not be reincarnated.
Secondly, although we can know from the following story that the death seal can be unlocked, only orochimaru knows. How could he tell Dou about it? Although Yakushi Kabuto and orochimaru stayed together for a long time, he never won the trust of orochimaru. After all, orochimaru is characterized by caution and suspicion. Huo Ying's soul of past dynasties can't be released, and it's impossible to carry out the next cycle.
Finally, take ten thousand steps back, assuming that Yakushi Kabuto really has the ability to unlock the death seal, and filth is reincarnated in past dynasties, it is estimated that he can't do it easily, otherwise he may face the situation of being smashed on the spot. Moreover, reincarnated ninjas are enough, and it is impossible to control the reincarnation of past dynasties. In a word, it is impossible for Yakushi Kabuto to get his hands on all the past generations of Huoying in Konoha Village, either because of his inability or for their own sake. After all, he wants to continue to live well and won't make trouble for himself.