Why does Kaido want Shuutenmaru to join him?

[Blackangel]

compared to kaido, shuutenmaru is nothing extraordinary.
why does kaido wants him to join his group?

 

[Kaname]

He is strong man.
Only the Yonko are on Kaido's level and they need strong people to maintain people around him.

 

[Blackangel]

yeah i think i understand it now
but shuutenmaru doesn't want to join kaido. he could have let him go.