All Supreme Kais died except Eastern Supreme Kai. Why new ones were not chosen?


Only Eastern Supreme Kai is left, why he does all the job? There's supposed to
be 4 Supreme Kais and 1 Grand Kai




We know the answer to this in the _Majin Buu Saga_ in Dragon Ball Z. While
Shin lived in the sacred world of the Kai's, _Bibidi_ (Note: Babidi's father),
targetted them and wanted to kill them. So he unleashed _Majin Buu_ (Note: Kid
Buu, his actual form) on them who ended up killing the North and West Supreme
Kai. Kid Buu apparently then absorbed the Southern Supreme Kai and ended up
transforming into _Super Buu_.

Finally, whle this monster went after _Shin and the Grand Supreme Kai_. The
Grand Supreme Kai intervened and was absorbed, which turned Buu into the _Fat
Majin Buu_ (The playful Buu we see the first time Babidi summons Buu). Hence
he spared Shin's life. Shin later caught Bibidi off guard and destroyed him
while Buu was in a ball and later hid the ball under the surface of the Earth.
Since all the 4 supreme Kai's had died, Shin became known as simply the
Supreme Kai who lived along with his body guard Kibito in the world of the
Kai's.

[This clip](https://www.youtube.com/watch?v=lxRb7h7xqHA) shows the scene where
Shin narrates the same.

With regard to why new Supreme Kai's weren't picked, there isn't a definite
explanation as to why. I believe this theory of multiple Supreme Kai's has
been retconned for the sake of simplicity. Here are a few reasons why

  * In the _Universe Survival Arc_ , we see only _1 Supreme Kai_ from every Universe and they are referred to as "Supreme Kai" and not "Grand Supreme Kai" .
  * The first reason indeed isn't completely factual but if you look at the episode where Goku, Beerus and Whis go to the _Sacred World of the Kai's_ in Universe 10, we see Gowasu with only his apprentice Zamasu. We don't see any other Supreme Kais. Also, it would make sense for Gowasu to train Zamasu to make him a Grand Supreme Kai. He was training to become a Supreme Kai. So if other Supreme Kais exist, they obviously could've trained him instead.
  * Shin is considered to be the _weakest and least experienced_ Supreme Kai compared to the Supreme Kais across the multiverse. It wouldn't make sense for them to recruit a few more Supreme Kais(More inexperienced than him, because if they were more experienced, they would end up becoming the _Grand Supreme Kai_.
  * Going back to the _Future Trunks Arc_. Zamasu only tried to kill Gowasu(In the present timeline). There is no mention of him trying to kill other Supreme Kai's in the same universe.
  * Finally the best reason why I think this theory has been completely retconned is based on _Episode 55_. In this Episode, Whis states that The "Kaioshin and Hakaishin(In Singular) are a set" when Goku asks was curious at to Beerus was concerned about Shin

Of course, this argument is indeed debatable and the only one who could give a
definite answer would be the writers themselves. However, based on the
information we have. I think it is fair to assume that this theory has been
retconned for simplicity reasons.

