It probably has to do with the big overhaul of the emergency missions. Basically, they added a lot of stuff to make upgrading knights easier for new players, like petite hearts, flower petals, blooming medicines, etc...
That doesn't seem to justify the increase when treasure rally event is rng-heavy and one nazupon roll could either give you several combos or none at all, and increased cost just makes it harder to complete and will require more farming than usual