My theory is Nasu gave Sakurai too much free reign in writing Koyan, so when he got delivered the ultimate turd that was Tunguska it was too late to change course and she just slammed the eject button on the entire thing. That's why we're back to old Koyanskaya in LB7 like nothing ever happened.
That's also why I think OC2 might actually be good. The rabid mutt appears to be on a leash after that truly abysmal performance.