Watergate has learned a lot from Jiuxin Nai, who is good at sealing technology. For example, Kyubi no Youko's ghouls and Bagua Yin were all learned from Jiuxin Milk. It can also be considered that Nagato may have learned a lot about sealing technology. If it's just a simple Kyubi no Youko seal, there's no need to use ghouls to seal yourself.
As shown above, when Kyubi no Youko attacked Konoha Village, he wanted to release Bijyudama to destroy Konoha. When Bijyudama was about to be released, Watergate used the technology of flying Raytheon to transfer Kyubi no Youko to explode outside the village. This transfer consumes a lot of chakra in Watergate, and he is obviously very tired. Later, he successfully pulled up the enchantment and suppressed Kyubi no Youko by using Jiu Si Nai chakra, but Jiu Si Nai was very weak after being extracted from Kyubi no Youko, and forced to open the enchantment to suppress nine dimensions, which was equivalent to ending his life as soon as possible.
As shown in the above picture, Sinatra has made up his mind to die in order to help Watergate seal Kyubi no Youko. In order to protect the village, let the children grow up healthily, and let Nagato stay and take care of Naruto after sealing Kyubi no Youko, she firmly chose to die. What a great mother and husband she is.
As shown above, Hisinai has a wish to see Naruto when he grows up. Watergate has always loved Jiusinai deeply, and he doesn't want Jiusinai's wish to be impossible. If you choose other ways to seal Kyubi no Youko in your body, you can't do this. Because the chakra in Kyubi no Youko is too big to be suppressed by physical methods, we have to seal a part of chakra with ghosts, and then seal chakra in Jiu Si and chakra in Kyubi no Youko into Naruto's body with gossip seal, so that Kyubi no Youko can be completely sealed. Watergate knows that if you want Jiu Si Nye to see Naruto when he grows up, you only need to seal chakra of Jiu Si Nye into Naruto, and you can see Naruto when Jiu Si Nye grows up at a certain time.
There is another reason besides spirit. Kyubi no Youko cannot be destroyed, but can only be sealed, because Kyubi no Youko is a weapon, in order to protect Konoha and balance the bijuu between villages.