I think they overestimated the value of the Haste gear tbh. Probably after the high prices of Skoll's Claws and Cassie Earrings in Eureka, they figured we'd happily farm Castrum 50+ times trying to chase that full Haste set. Unlike Eureka however, it's simply a small dps boost and doesn't affect your survival rate at all, so unless the dps checks in the Savage mode of next stage are so high that even dps lost actions aren't enough, it's not worth the effort.

Mettle isn't worth it because Bozjan exp is largely worthless after rank 10 right now and reaching 15 just means a higher penalty on death.

Regular exp would have to outweigh the equivalent of doing Fates and Skirmishes in that same time.

Memories aren't worth it because they decided faceroll HW FATEs should rain them down on us.

Dropping more fragments doesn't help that much, they're already very cheap on the mb. Clusters wouldn't work since you can farm them anytime.

They've locked themselves into a corner really where they have to buff the rewards to silly amounts to make it worth looking at. Almost everything in Bozja including the Relic is handed over on a plate already.