Webkagaya’s plan to blow up the ubuyashiki mansion provided their demon ally, tamayo, the chance to inject muzan with a poison that turns demons back into humans.
Webin a flashback scene, it is revealed that the plan was orchestrated by ubuyashiki with only himejima as a confidant since the other hashiras wouldn’t have.
Webit is then discovered that blowing up the estate wasn’t muzan’s plan but ubuyashiki’s.
It left muzan in turmoil, delaying his regeneration and buying the hashira.