TLDR: It didnt matter if Shiabatsu or Seiken takes the throne, apparently BOTH were going to not care for the Spider or aid the Spider's goals and Kanpeki says "If I cant have the empire, then no one can."
Because remember, the "Progressive/Traditionalist" conflict REALLY mattered
We could have dominated and we would still be thrown under the bus.
Thrown under the bus? My good man, we get to be the main villains this arc! This is the most exciting thing to happen since Daigotsu ascended.
The Story Team is at last giving the Spider what we've wanted all along. Some of us wanted to be Horde. Others (like me) wanted to be a Great Clan. But we all
wanted to be the bad guys. That's what the Spider are supposed to be all about anyways, but we haven't been the main villains of an arc since Samurai Edition.
But yeah, I really like to think we were worth more than that to our man Shibatsu. Kanpeki even dressed him up like Daigotsu, for crying out loud.
But maybe now that Seiken has been chosen, Shibatsu will fall firmly back in our camp once more.