Because they hoped to milk whales even with treasures BLATANTLY made for f2p only.

That's why they merged two treasures together and they removed mei (mei was the other common rare in edo yagura treasure) while also cutting by half the duration of the treasure (in cn they stay up 1 month, not two weeks only), but they behave like if we did not know how the things work here and in CN, so they only managed to make some whale waste their previously hoarded reserves of ss, but no competitive f2p or low casher is so mad to go in a treasure that was modified in comparison with CN knowing it will appear again next month or in another future event if there is no rebate available linked to it.