Zoro has clearly yet to master Enma fully, that's why he could not land his big Enma attack last chapter and was quite drained after using it.
King match-up allows Zoro to master Enma, and then get back to the Kaido fight and open Kaido's scar.
I don't know how Zoro will be driven into fighting King yet, that remains to be seen. It obviously not going to be him bailing the fight with Kaido out of nowhere